Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Total gross revenues	$ 83,315	$ 84,514	$ 81,792	$ 80,827	$ 83,036	$ 81,550	$ 80,135	$ 81,248	$ 330,448	$ 325,969	$ 396,971
Net income	105,222	43,618	19,131	18,420	85,423	147,821	23,769	28,280	186,391	285,293	230,906
Net income attributable to common shareholders	$ 102,712	$ 40,285	$ 17,254	$ 16,536	$ 83,574	$ 141,560	$ 21,721	$ 26,405	$ 176,788	$ 273,225	$ 220,838
Net income attributable to common shareholders - basic (usd per share)	$ 0.37	$ 0.15	$ 0.07	$ 0.07	$ 0.34	$ 0.60	$ 0.09	$ 0.11	$ 0.66	$ 1.15	$ 0.93
Net income attributable to common shareholders - per common share diluted (usd per share)	$ 0.37	$ 0.15	$ 0.06	$ 0.06	$ 0.33	$ 0.59	$ 0.09	$ 0.11	$ 0.66	$ 1.15	$ 0.93