Lease Obligations - Future Sublease Payments for Ground Lease Rentals (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Finance lease(1)	$ 13,887	$ 14,382
2019 remaining	17,318	22,528
2020	21,766	20,903
2021	19,708	18,886
2022	17,970	17,245
2023	15,839	15,128
2024	10,733
Thereafter	33,922	43,439
Total	$ 137,256	$ 138,129