Segment Reporting - Reconciliation of Net Income To Adjusted Segment Earnings before Interest, Taxes, Depreciation and Amortization (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net income	$ 23,724	$ 44,333	$ 43,609	$ 38,945	$ 66,888	$ 32,214	$ (5,156)	$ 14,016	$ 150,611	$ 107,962	$ 85,520
Income tax provision (benefit)	7,834	19,964	14,113	15,270	(38,458)	9,197	527	7,877	57,181	(20,857)	42,283
Interest income and other	(2,903)	(1,400)	(2,474)	1,800	(452)	(1,103)	(1,592)	(605)	(4,977)	(3,752)	(10,466)
Interest expense	7,076	7,246	6,583	6,244	$ 6,547	$ 6,760	$ 6,250	$ 5,801	27,149	25,358	24,819
Gain on sale of business	0	(13,031)	0	0					(13,031)	0	0
Gain on sale of business	$ 9,072	$ 0	$ 0	$ 0					9,072	0	0
Adjusted Segment EBITDA									358,741	267,435	285,944
Segment Reconciling Items
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net income									150,611	107,962	85,520
Income tax provision (benefit)									57,181	(20,857)	42,283
Interest income and other									(4,977)	(3,752)	(10,466)
Interest expense									27,149	25,358	24,819
Gain on sale of business									(13,031)	0	0
Gain on sale of business									9,072	0	0
Unallocated corporate expenses									96,595	83,140	88,182
Segment depreciation expense									27,979	27,112	34,064
Amortization of other intangible assets									8,162	10,563	10,306
Segment special charges									0	37,207	9,833
Remeasurement of acquisition-related contingent consideration									0	702	1,403
Adjusted Segment EBITDA									$ 358,741	$ 267,435	$ 285,944