Summary of Quarterly Results (unaudited) - Summary of Quarterly Results of Operations (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 Data [Abstract]
Revenues	$ 190,675	$ 192,596	$ 191,419	$ 184,271	$ 180,257	$ 179,770	$ 177,704	$ 181,236	$ 758,961	$ 718,967	$ 683,341
Net income (loss) attributable to the common stockholders	$ 5,318	$ 37,531	$ (34,816)	$ 1,114	$ (6,793)	$ (10,214)	$ 103,016	$ 372	$ 9,147	$ 86,381	$ (9,934)
Income (Loss) Per Common Share Basic	$ 0.02	$ 0.16	$ (0.14)	$ 0.00	$ (0.03)	$ (0.04)	$ 0.44	$ 0.00	$ 0.04	$ 0.37	$ (0.05)
Income (Loss) Per Common Share Diluted	$ 0.02	$ 0.16	$ (0.14)	$ 0.00	$ (0.03)	$ (0.04)	$ 0.44	$ 0.00	$ 0.04	$ 0.37	$ (0.05)