Debt and Other Obligations - Refinancing of Credit Agreement and Term B Borrowings (Details)		1 Months Ended	9 Months Ended
	Mar. 06, 2018 USD ($)	May 31, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Debt and Other Obligations
Outstanding amount of debt			$ 513,180,000		$ 510,492,000
Letters of credit outstanding amount			5,100,000
Payment of debt issuance costs		$ 200,000	$ 0	$ 214,000
London Interbank Offered Rate (LIBOR)
Debt and Other Obligations
Minimum interest base (as a percent)		1.00%
London Interbank Offered Rate (LIBOR) | Maximum
Debt and Other Obligations
Increase in margin (as a percent)		3.75%
Fiscal quarters ended June 30, 2021 through September 30, 2021
Debt and Other Obligations
Consolidated leverage ratio		500.00%
December 31, 2021 and the last day of each fiscal quarter thereafter
Debt and Other Obligations
Consolidated leverage ratio		475.00%
Loans Payable
Debt and Other Obligations
Outstanding amount of debt	$ 505,000,000
Weighted average interest rate			3.50%
Revolving Credit Facility
Debt and Other Obligations
Maximum borrowing capacity	605,000,000
Letters of credit outstanding amount			$ 100,000,000
Increase in additional borrowing capacity	$ 125,000,000
Leverage ratio to increase credit commitment	3.80
Available borrowing capacity			$ 94,900,000
Increase in margin (as a percent)	50.00%
Interest rate in excess of applicable rate upon acceleration and default (as a percent)	2.00%
Revolving Credit Facility | Minimum
Debt and Other Obligations
Unused commitment fee (as a percent)	0.375%
Revolving Credit Facility | Maximum
Debt and Other Obligations
Unused commitment fee (as a percent)	0.50%
Revolving Credit Facility | Fed Funds Effective Rate Overnight Index Swap Rate
Debt and Other Obligations
Interest rate margin (as a percent)	0.50%
Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Debt and Other Obligations
Interest rate margin (as a percent)	1.00%
Revolving Credit Facility | Fiscal quarters ended June 30, 2021 through March 31, 2022
Debt and Other Obligations
Consolidated leverage ratio	425.00%
Revolving Credit Facility | Fiscal quarters ended June 30, 2022 and the last day of each fiscal quarter thereafter
Debt and Other Obligations
Consolidated leverage ratio	375.00%
Revolving Credit Facility | Last day of any fiscal quarter
Debt and Other Obligations
Consolidated leverage ratio	275.00%
Revolving Credit Facility | Revolving Credit Facility
Debt and Other Obligations
Maximum borrowing capacity	$ 100,000,000