Acquisitions - Unaudited Supplemental Pro Forma Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Combinations [Abstract]
Revenues	$ 3,004,888	$ 2,655,029	$ 8,126,257	$ 7,335,868
Gross profit	433,432	369,629	1,086,411	1,019,842
Selling, general and administrative expenses	226,017	210,503	653,444	631,254
Amortization of intangible assets	12,182	12,133	36,803	37,252
Net income	127,593	93,185	246,773	214,717
Net income attributable to common stock	$ 127,245	$ 92,649	$ 245,087	$ 213,485
Earnings per share attributable to common stock:
Basic (in dollars per share)	$ 0.83	$ 0.58	$ 1.59	$ 1.35
Diluted (in dollars per share)	$ 0.83	$ 0.58	$ 1.58	$ 1.34