Segment Reporting - Reconciliation of Net Income to Adjusted Segment Earnings before Interest, Taxes, Depreciation and Amortization (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net income	$ 38,945	$ 14,016
Income tax provision	15,270	7,877
Interest income and other	1,800	(605)
Interest expense	6,244	5,801
Total Adjusted Segment EBITDA	95,281	56,017
Segment Reconciling Items
Segment Reporting, Other Significant Reconciling Item [Line Items]
Net income	38,945	14,016
Income tax provision	15,270	7,877
Interest income and other	1,800	(605)
Interest expense	6,244	5,801
Unallocated corporate expenses	23,888	19,053
Segment depreciation expense	6,864	7,216
Amortization of intangible assets	2,270	2,493
Remeasurement of acquisition-related contingent consideration	0	166
Total Adjusted Segment EBITDA	$ 95,281	$ 56,017