Business Segment Information - Reconciliation of Segment Profit to Income Before Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reconciliation of segment profit to income before income taxes
Income before income taxes	$ 44,975	$ 43,940	$ 84,838	$ 83,271
Stock compensation expense	10,323	9,176	31,834	27,573
Changes in fair value of contingent consideration	(834)	313	(631)	510
Impairment of intangible assets		0		4,800
Non-controlling interest segment (profit) loss	(788)	194	59	1,341
Depreciation and amortization	28,189	26,885	82,896	77,472
Interest expense	7,663	3,038	16,711	6,780
Interest and other income	(1,781)	(741)	(3,801)	(2,116)
Segment Profit	$ 87,747	$ 82,805	$ 211,906	$ 199,631