Long-Term Debt - Other Long-Term Debt (Details) - Wells Fargo Bank N.A. - Line of credit $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Aug. 01, 2016 USD ($)	Dec. 31, 2009 agreement
Other Long-Term Debt
Number of credit agreements | agreement				2
Revolving credit facility | Revolver
Other Long-Term Debt
Borrowing base			$ 425.0
Cash balance threshold			$ 30.0
Average interest rate (as a percent)	2.59%	2.67%
Average outstanding balance	$ 195.2	$ 143.1
Total interest and commitment fees	$ 1.5	$ 1.3
Covenant, total leverage ratio	4.0
Covenant, current ratio	1.00
Total leverage ratio	3.73
Current ratio	2.88
Revolving credit facility | London Interbank Offered Rate (LIBOR) | Minimum | Revolver
Other Long-Term Debt
Margin interest rate (as a percent)	1.50%
Revolving credit facility | London Interbank Offered Rate (LIBOR) | Maximum | Revolver
Other Long-Term Debt
Margin interest rate (as a percent)	2.50%
Revolving credit facility | Federal Funds Effective Swap Rate | Revolver
Other Long-Term Debt
Margin interest rate (as a percent)	0.50%
Revolving credit facility | One Month Adjust LIBO Rate | Revolver
Other Long-Term Debt
Margin interest rate (as a percent)	1.00%
Revolving credit facility | Base rate | Minimum | Revolver
Other Long-Term Debt
Margin interest rate (as a percent)	0.50%
Revolving credit facility | Base rate | Maximum | Revolver
Other Long-Term Debt
Margin interest rate (as a percent)	1.50%