Long-term Debt - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Nov. 04, 2016	May 16, 2016
Debt Instrument [Line Items]
Amortization of debt issuance costs	$ 500,000	$ 300,000	$ 300,000
Unamortized debt issuance costs	2,300,000	1,200,000
Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility, average borrowings	184,400,000	39,600,000
Revolving credit facility, minimum amount borrowed	0	0
Revolving credit facility, maximum amount borrowed	$ 428,000,000	$ 120,900,000
Revolving credit facility, weighted-average interest rate	1.70%	1.60%
Total unused facility fees and letter of credit participation fees	$ 700,000	$ 600,000	$ 700,000
Ninth Amendment | Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility maximum borrowing capacity				$ 600,000,000
Revolving credit facility, potentially additional borrowing capacity				100,000,000
Seventh Amendment | Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility maximum borrowing capacity					$ 300,000,000
Eighth Amendment | Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility maximum borrowing capacity				$ 450,000,000	450,000,000
Fee amount					$ 1,300,000