Other Assets and Accrued Liabilities - Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Prepaid rent	$ 10,058				$ 10,519
Prepaid maintenance expenses	3,546				3,062
Interest rate swaps	5,447				2,411
Deferred contract asset	35,617				0
Other	8,715				1,119
Prepaid expenses and other	$ 63,383	$ 59,407	$ 58,459	$ 46,987	$ 17,111