Selected Quarterly Data Summary of Selected Quarterly Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 1,748,919	$ 1,831,732	$ 1,838,070	$ 1,773,912	$ 1,684,131	$ 1,721,024	$ 1,709,132	$ 1,625,777	$ 7,192,633	$ 6,740,064	$ 5,062,528
Gross margin	697,327	712,779	723,944	699,479	664,559	664,411	671,059	651,884	2,833,529	2,651,913	2,075,402
Operating income	151,671	166,745	200,285	185,926	146,250	156,188	173,596	173,834	704,627	649,868	530,180
Net income	$ 95,060	$ 101,346	$ 119,722	$ 107,095	$ 80,469	$ 91,515	$ 104,882	$ 104,653	$ 423,223	$ 381,519	$ 311,623
Basic earnings per share	$ 0.31	$ 0.33	$ 0.39	$ 0.35	$ 0.27	$ 0.30	$ 0.35	$ 0.35
Diluted earnings per share	$ 0.31	$ 0.33	$ 0.39	$ 0.35	$ 0.26	$ 0.30	$ 0.34	$ 0.34