Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 578,522	$ 575,982	$ 569,239	$ 560,792	$ 555,292	$ 550,500	$ 530,512	$ 522,326	$ 2,284,535	$ 2,158,628	$ 2,045,255
Net income	385,636	192,407	254,543	141,590	237,486	238,199	165,194	235,781	974,175	876,660	1,033,708
Net income attributable to common stockholders	$ 385,734	$ 192,486	$ 254,662	$ 141,643	$ 237,573	$ 238,248	$ 165,225	$ 235,875	$ 974,525	$ 876,921	$ 1,034,002
Net income per common share - basic (in dollars per share)	$ 2.79	$ 1.39	$ 1.84	$ 1.03	$ 1.72	$ 1.73	$ 1.20	$ 1.72	$ 7.05	$ 6.36	$ 7.53
Net income per common share - diluted (in dollars per share)	$ 2.79	$ 1.39	$ 1.84	$ 1.03	$ 1.72	$ 1.72	$ 1.20	$ 1.72	$ 7.05	$ 6.35	$ 7.52