Quarterly Results of Operations (Unaudited) (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	$ 180,281	$ 170,389	$ 174,091	$ 180,128	$ 179,825	$ 170,783	$ 160,747	$ 154,029	$ 704,889	$ 665,384	$ 675,323
Income from continuing operations	58,084	49,740	12,942	45,299	109,245	57,770	44,460	37,331	166,065	248,806	339,016
Discontinued operations	115,832	104,332	7,948	98,426	22,579	3,389	8,358	6,913	326,538	41,239	27,129
Net income	$ 173,916	$ 154,072	$ 20,890	$ 143,725	$ 131,824	$ 61,159	$ 52,818	$ 44,244	$ 492,603	$ 290,045	$ 366,145
Net income available to common shareholders - basic (USD per share/unit)	$ 1.15	$ 1.02	$ 0.13	$ 0.95	$ 0.87	$ 0.41	$ 0.35	$ 0.29	$ 3.26	$ 1.92	$ 2.44
Income per common share - diluted (USD per share/unit)	$ 1.14	$ 1.01	$ 0.13	$ 0.95	$ 0.87	$ 0.40	$ 0.35	$ 0.29	$ 3.24	$ 1.91	$ 2.43