Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 83,036	$ 81,550	$ 80,135	$ 81,248	$ 88,182	$ 100,295	$ 105,673	$ 102,821	$ 325,969	$ 396,971	$ 392,690
Net income (loss)	85,423	147,821	23,769	28,280	25,674	220,850	(795)	(14,823)	285,293	230,906	86,629
Net income attributable to common shareholders	$ 83,574	$ 141,560	$ 21,721	$ 26,405	$ 23,796	$ 216,190	$ (3,327)	$ (15,957)	$ 273,225	$ 220,838	$ 79,067
Net income attributable to common shareholders - basic (usd per share)	$ 0.34	$ 0.60	$ 0.09	$ 0.11	$ 0.10	$ 0.91	$ (0.01)	$ (0.07)	$ 1.15	$ 0.93	$ 0.33
Net income (loss) attributable to common shareholders - per common share diluted (usd per share)	$ 0.33	$ 0.59	$ 0.09	$ 0.11	$ 0.10	$ 0.90	$ (0.01)	$ (0.07)	$ 1.15	$ 0.93	$ 0.33