Business Segment Information - Reconciliation of Segment Profit to Income Before Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of segment profit to income before income taxes
Income (loss) from continuing operations before income taxes	$ (36,331)	$ (19,626)	$ 10,780	$ 4,692	$ 15,306	$ 4,903	$ 12,950	$ (11,400)	$ (40,485)	$ 21,759	$ 33,633
Stock compensation expense	7,341	5,442	6,592	5,797	5,462	4,604	5,207	9,400	25,172	24,673	28,936
Changes in fair value of contingent consideration											1,108
Depreciation and amortization	26,411	24,730	23,888	23,358	27,869	28,890	28,191	25,417	98,387	110,367	112,284
Interest expense	6,626	7,286	7,995	8,958	8,826	8,935	9,070	9,037	30,865	35,868	35,180
Interest and other income	(1,935)	(349)	(551)	$ (1,219)	$ (1,578)	$ (1,699)	$ (1,821)	$ (1,759)	(4,054)	(6,857)	(4,884)
Special charges	$ 9,170	$ 16,599	$ 8,309						34,078
Segment Profit (Loss)									$ 143,963	$ 185,810	$ 206,257