Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 2,673,632	$ 2,823,176	$ 2,782,449	$ 2,608,355	$ 2,672,602	$ 2,800,569	$ 2,726,480	$ 2,432,854	$ 10,887,612	$ 10,632,505	$ 9,937,889
Gross profit	389,181	406,668	410,119	389,101	380,133	398,382	391,573	363,884	1,595,069	1,533,972	$ 1,447,938
Net income	$ 30,828	$ 35,366	$ 46,580	$ 34,291	$ (33,387)	$ 45,261	$ 46,310	$ 35,815	$ 147,065	$ 93,999
Basic earnings per common share	$ 1.44	$ 1.65	$ 2.12	$ 1.47	$ (1.41)	$ 1.88	$ 1.91	$ 1.47	$ 6.67	$ 3.91	$ 3.82
Diluted earnings per common share	$ 1.44	$ 1.65	$ 2.12	$ 1.47	$ (1.41)	$ 1.88	$ 1.91	$ 1.47	$ 6.67	$ 3.90	$ 3.60