Subsidiary Guarantors - Senior Notes (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	May. 02, 2013 USD ($)	Nov. 02, 2010 USD ($)
Senior Notes [Line Items]
Carrying value of senior notes		$ 542,740,000	$ 550,000,000
Event of default for senior notes - not discharged, bonded or insured judgment in excess of this amount	$ 50,000,000.0
Event of default for senior notes - failure of other debt payment at maturity in excess of this amount	$ 50,000,000.0
Debt Instrument, Covenant, Total Leverage Ratio Maximum, Ability to Repurchase Stock, Notes, or Pay Dividends		2.5
Debt Instrument, Covenant, Total Leverage Ratio Maximum, Ability to Repurchase Stock, Notes, or Pay Dividends, Dividend Exception Amount		$ 20,000,000
Our ownership percentage of subsidiary guarantors of senior notes	100.00%
Senior Notes Due 2020 [Member]
Senior Notes [Line Items]
Carrying value of senior notes	$ 292,740,000	292,740,000	300,000,000		$ 300,000,000.0
Debt instrument, repurchase amount		$ 7,300,000
Interest rate of senior notes		6.625%
Repayments of Long-term Debt					$ 200,000,000
Senior notes, redemption price, percentage		99.50%
Percentage of original aggregate principle amount of senior notes included in repurchase price at change of control	101.00%
Senior Notes Due 2020 [Member] | Senior Notes, Redemption, Period One [Member]
Senior Notes [Line Items]
Senior notes, redemption price, percentage		103.313%
Senior Notes Due 2021 [Member]
Senior Notes [Line Items]
Carrying value of senior notes		$ 250,000,000	$ 250,000,000	$ 250,000,000
Interest rate of senior notes		4.75%
Proceeds to repurchase shares of common stock				$ 200,000,000.0
Percentage of original aggregate principle amount of senior notes included in repurchase price at change of control	101.00%
Senior Notes Due 2021 [Member] | Senior Notes, Redemption, Period One [Member]
Senior Notes [Line Items]
Senior notes, redemption price, percentage		103.563%