Selected Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 1,175,230	$ 1,105,999	$ 1,069,372	$ 1,023,961	$ 945,239	$ 905,089	$ 889,163	$ 869,791	$ 875,575	$ 4,374,562	$ 3,609,282	$ 3,204,577
Gross profit	363,381	314,980	315,847	297,098	249,372	242,451	245,735	245,858
Net income	$ 48,421	$ 31,822	$ 29,471	$ 2,689	$ 7,897	$ 7,675	$ 6,164	$ (4,584)	$ 35,219	$ 112,403	$ 17,152	$ 226,126
Basic (in dollars per share)	$ 0.81	$ 0.54	$ 0.51	$ 0.05	$ 0.14	$ 0.14	$ 0.11	$ (0.08)		$ 1.93	$ 0.31	$ 4.28
Diluted (in dollars per share)	$ 0.79	$ 0.52	$ 0.49	$ 0.05	$ 0.13	$ 0.13	$ 0.11	$ (0.08)		$ 1.85	$ 0.29	$ 4.16