Debt (Details) - USD ($)		3 Months Ended	6 Months Ended
	Jul. 31, 2015	Jun. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Credit facility
Less: Amounts due within one year		$ 4,250,000	$ 4,250,000	$ 4,250,000
Total long-term debt due after one year		405,123,000	405,123,000	406,286,000
Accretion of debt financing costs included in interest expense		500,000	1,000,000
Credit Facility | Alternate base rate
Credit facility
Margin of interest (as a percent)	3.75%
Credit Facility | LIBOR
Credit facility
Margin of interest (as a percent)	4.75%
Variable rate base minimum (as a percent)	1.00%
Term Loan
Credit facility
Total Term Loan outstanding		409,373,000	409,373,000	410,536,000
Less: Amounts due within one year		4,250,000	4,250,000	4,250,000
Total long-term debt due after one year		405,123,000	405,123,000	$ 406,286,000
Debt issuance costs incurred	$ 12,900,000
Deferred issuance costs, net		11,300,000	11,300,000
Face amount	$ 425,000,000
Amortization per year (as a percent)	1.00%
Revolving loan
Credit facility
Debt issuance costs incurred	$ 1,300,000
Maximum borrowing available	25,000,000
Letter-of-credit sub-facility
Credit facility
Maximum borrowing available	$ 10,000,000	600,000	600,000
Letters of credit, amount outstanding		$ 0	$ 0