Other Assets and Accrued Liabilities - Current Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Other Liabilities Disclosure [Abstract]
Prepaid rent	$ 0		$ 11,245
Prepaid maintenance expenses	3,915		3,981
Interest rate swaps	4,054		4,930
Contract asset	41,195		37,957
Other	3,369		2,049
Prepaid expenses and other	$ 52,533	$ 48,582	$ 60,162