Selected Quarterly Information (Unaudited) (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
Selected Quarterly Information (Unaudited)
Total revenues	$ 361,074	$ 376,109	$ 393,990	$ 385,458	$ 397,151	$ 409,558	$ 400,634	$ 390,416	$ 1,516,631	$ 1,597,759	$ 1,370,354
Net income	$ 62,920	$ 48,058	$ 67,445	$ 67,113	$ 80,893	$ 74,586	$ 82,988	$ 74,864	$ 245,536	$ 313,331	$ 252,998
Net income per share, basic and diluted (in dollars per share)	$ 0.76	$ 0.58	$ 0.80	$ 0.80	$ 0.97	$ 0.89	$ 0.98	$ 0.88	$ 2.94	$ 3.71	$ 2.96