Annual report pursuant to Section 13 and 15(d)

Borrowings (6.125% Senior Notes) (Narrative) (Details)

v3.8.0.1
Borrowings (6.125% Senior Notes) (Narrative) (Details) - 6.125% senior unsecured notes due 2024 - USD ($)
May 19, 2017
Oct. 03, 2016
Dec. 31, 2017
Sep. 30, 2017
Debt Instrument, Redemption [Line Items]        
Debt instrument aggregate principal amount $ 200,000,000 $ 400,000,000    
Debt instrument, interest rate, stated (as a percent) 6.125% 6.125% 6.125% 6.125%
Debt instrument maturity date   Oct. 01, 2024    
Debt instrument repayment beginning date   Apr. 01, 2017    
Net proceeds from issuance of senior unsecured notes   $ 391,270,000    
Debt instrument redemption price percent (as a percent) 104.125%      
Proceeds from issuance of debt $ 206,139,000      
Change Of Control        
Debt Instrument, Redemption [Line Items]        
Debt instrument redemption price percent (as a percent)   101.00%    
Prior to October 1, 2019, a Redemption of up to 35% of the Principal        
Debt Instrument, Redemption [Line Items]        
Debt instrument redemption price percent (as a percent)   106.125%    
Number of days to closing date of equity offerings   180 days    
Prior to October 1, 2019, a Redemption of All or Part of the Principal        
Debt Instrument, Redemption [Line Items]        
Debt instrument redemption price percent (as a percent)   100.00%    
On or After October 1, 2019, but Before October 1, 2020        
Debt Instrument, Redemption [Line Items]        
Debt instrument redemption price percent (as a percent)   104.594%    
On or After October 1, 2020, but Before October 1, 2021        
Debt Instrument, Redemption [Line Items]        
Debt instrument redemption price percent (as a percent)   103.063%    
On or After October 1, 2021, but Before October 1, 2022        
Debt Instrument, Redemption [Line Items]        
Debt instrument redemption price percent (as a percent)   101.531%    
On or After October 1, 2022        
Debt Instrument, Redemption [Line Items]        
Debt instrument redemption price percent (as a percent)   100.00%    
Maximum | Prior to October 1, 2019, a Redemption of up to 35% of the Principal        
Debt Instrument, Redemption [Line Items]        
Redemption principal amount percentage (as a percent)   35.00%    
Minimum | Prior to October 1, 2019, a Redemption of up to 35% of the Principal        
Debt Instrument, Redemption [Line Items]        
Redemption principal remaining amount percentage (as a percent)   65.00%