Long-term Debt - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	May 16, 2016	Jan. 11, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Amortization of debt issuance costs	$ 100,000	$ 100,000	$ 200,000	$ 200,000
Unamortized debt issuance costs	2,000,000		2,000,000				$ 1,200,000
Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility, maximum borrowing capacity	450,000,000		450,000,000		$ 300,000,000
Revolving credit facility, potential additional borrowing capacity	150,000,000		150,000,000
Revolving credit facility, average borrowings	109,600,000	37,000,000	93,800,000	33,700,000
Minimum amount borrowed at any one time outstanding	0	0	0	0
Maximum amount borrowed at any one time outstanding	$ 220,000,000	$ 120,900,000	$ 220,000,000	$ 120,900,000
Revolving credit facility, weighted-average interest rate	1.70%	1.80%	1.80%	1.70%
Total unused facility fees and letter of credit participation fees	$ 200,000	$ 100,000	$ 400,000	$ 300,000
Revolving Credit Facility | Eighth Amendment
Debt Instrument [Line Items]
Revolving credit facility, maximum borrowing capacity					$ 450,000,000
Incurred fees in connection with the Sixth Amendment						$ 600,000