Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 3,285,755	$ 2,984,859	$ 2,785,464	$ 2,636,635	$ 2,477,541	$ 2,290,188	$ 2,105,204	$ 1,957,736	$ 11,692,713	$ 8,830,669	$ 6,779,511
Gross profit	1,178,401	991,879	883,156	979,611	823,122	757,344	632,106	588,196
Net income	$ 185,517	$ 129,590	$ 65,600	$ 178,222	$ 66,748	$ 51,517	$ 40,755	$ 27,658	$ 558,929	$ 186,678	$ 122,641
Earnings (loss) per share:
Basic (in USD per share)	$ 0.43	$ 0.30	$ 0.15	$ 0.41	$ 0.16	$ 0.12	$ 0.10	$ 0.06	$ 1.29	$ 0.44	$ 0.29
Diluted (in USD per share)	$ 0.41	$ 0.29	$ 0.15	$ 0.40	$ 0.15	$ 0.12	$ 0.09	$ 0.06	$ 1.25	$ 0.43	$ 0.28