Other Assets and Accrued Liabilities - Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Prepaid rent	$ 11,245				$ 10,519
Prepaid maintenance expenses	3,981				3,062
Interest rate swaps	4,930				2,411
Deferred contract costs	37,957				0
Other	2,049				1,119
Prepaid expenses and other	$ 60,162	$ 59,407	$ 58,459	$ 46,987	$ 17,111