Supplemental Selected Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Selected Quarterly Financial Information [Abstract]
Total revenues	$ 362,965	$ 401,950	$ 385,112	$ 357,572	$ 309,822	$ 328,334	$ 323,961	$ 303,247	$ 1,507,599	$ 1,265,364	$ 1,200,301
Net (loss) income	15,956	(175,570)	15,157	(894)	24,959	27,478	20,114	15,359	(145,351)	87,910	65,981
Net (loss) income attributable to controlling interests and available to common shareholders	$ 15,954	$ (175,561)	$ 15,158	$ (901)	$ 24,969	$ 27,490	$ 20,148	$ 15,384	$ (145,350)	$ 87,991	$ 67,080
Net (loss) income per common share – basic	$ 0.34	$ (3.84)	$ 0.33	$ (0.02)	$ 0.55	$ 0.61	$ 0.45	$ 0.34	$ (3.19)	$ 1.95	$ 1.50
Net (loss) income per common share – diluted	$ 0.34	$ (3.84)	$ 0.33	$ (0.02)	$ 0.54	$ 0.60	$ 0.44	$ 0.34	$ (3.19)	$ 1.92	$ 1.48
Depreciation, accretion and amortization excluded									$ 148,004	$ 107,524	$ 103,494