Selected Quarterly Financial 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]
Total revenues	$ 1,823,333	$ 1,738,355	$ 1,644,694	$ 1,573,129	$ 1,484,728	$ 1,409,432	$ 1,340,407	$ 1,270,089	$ 6,779,511	$ 5,504,656	$ 4,374,562
Gross profit	573,968	564,397	522,942	526,728	470,396	455,038	425,559	400,903
Net income	$ 43,178	$ 29,432	$ 26,335	$ 23,696	$ 83,371	$ 59,295	$ 71,018	$ 53,115	$ 122,641	$ 266,799	$ 112,403
Earnings (loss) per share:
Basic (in USD per share)	$ 0.10	$ 0.07	$ 0.06	$ 0.06	$ 0.20	$ 0.14	$ 0.17	$ 0.13	$ 0.29	$ 0.63	$ 0.28
Diluted (in USD per share)	$ 0.10	$ 0.07	$ 0.06	$ 0.05	$ 0.19	$ 0.14	$ 0.16	$ 0.12	$ 0.28	$ 0.62	$ 0.26