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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net income	$ 66,888	$ 32,214	$ (5,156)	$ 14,016	$ 7,101	$ 21,691	$ 26,547	$ 30,181	$ 107,962	$ 85,520	$ 66,053
Income tax provision (benefit)	(38,458)	9,197	527	7,877	(1,832)	10,292	15,437	18,386	(20,857)	42,283	39,333
Interest income and other	(452)	(1,103)	(1,592)	(605)	(571)	(3,213)	(4,125)	(2,557)	(3,752)	(10,466)	(3,232)
Interest expense	$ 6,547	$ 6,760	$ 6,250	$ 5,801	$ 5,983	$ 6,304	$ 6,303	$ 6,229	25,358	24,819	42,768
Loss on early extinguishment of debt									0	0	19,589
Adjusted Segment EBITDA									267,435	285,944	283,435
Segment Reconciling Items
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net income									107,962	85,520	66,053
Income tax provision (benefit)									(20,857)	42,283	39,333
Interest income and other									(3,752)	(10,466)	(3,232)
Interest expense									25,358	24,819	42,768
Loss on early extinguishment of debt									0	0	19,589
Unallocated corporate expenses									83,140	88,182	81,348
Segment depreciation expense									27,112	34,064	27,717
Amortization of intangible assets									10,563	10,306	11,726
Segment special charges									37,207	9,833	0
Remeasurement of acquisition-related contingent consideration									702	1,403	(1,867)
Adjusted Segment EBITDA									$ 267,435	$ 285,944	$ 283,435