Debt and Other Obligations - Refinancing of Credit Agreement and Term B Borrowings (Details) $ in Thousands		1 Months Ended				9 Months Ended
	Mar. 06, 2018 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	May 31, 2020	Mar. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt and Other Obligations
Outstanding amount of debt		$ 529,189				$ 529,189	$ 507,201
Letters of credit outstanding amount		$ 5,200				5,200
Debt issuance costs						$ 214
LIBOR | Minimum
Debt and Other Obligations
Minimum interest base				1.00%
LIBOR | Maximum
Debt and Other Obligations
Increase in margin(as a percent)				3.75%
Fiscal quarters ended June 30, 2020 through March 31, 2021
Debt and Other Obligations
Consolidated leverage ratio				5.25%
Fiscal quarters ended June 30, 2021 through September 30, 2021
Debt and Other Obligations
Consolidated leverage ratio				5.00%
December 31, 2021 and the last day of each fiscal quarter thereafter
Debt and Other Obligations
Consolidated leverage ratio				4.75%
Credit Agreement, dated March 6, 2018, Term Loan B
Debt and Other Obligations
Outstanding amount of debt	$ 505,000
Weighted average interest rate		3.60%				3.60%
Revolving credit facility
Debt and Other Obligations
Borrowing		$ 22,000	$ 57,000		$ 79,000
Available borrowing capacity		94,800				$ 94,800
Maximum borrowing capacity	605,000
Letters of credit outstanding amount		$ 100,000				$ 100,000
Increase in additional borrowing capacity	$ 125,000
Leverage ratio to increase credit commitment	3.80
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 | LIBOR
Debt and Other Obligations
Interest rate margin (as a percent)	1.00%
Revolving credit facility | Federal funds rate
Debt and Other Obligations
Interest rate margin (as a percent)	0.50%
Revolving credit facility | Fiscal quarters ended June 30, 2020 through March 31, 2021
Debt and Other Obligations
Consolidated leverage ratio	4.50%
Revolving credit facility | Fiscal quarters ended June 30, 2021 through March 31, 2022
Debt and Other Obligations
Consolidated leverage ratio	4.25%
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	3.75%
Revolving credit facility | Last day of any fiscal quarter
Debt and Other Obligations
Consolidated leverage ratio	2.75%
Revolving credit facility | Revolving credit facility
Debt and Other Obligations
Maximum borrowing capacity	$ 100,000