Lease Obligations - Future Sublease Payments for Ground Lease Rentals (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2019 remaining	$ 82,090
2020	324,700
2021	277,508
2022	223,929
2023	177,033
2024	129,957
Thereafter	412,103
Total	1,627,320
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Finance lease		$ 14,382
2019		22,528
2020		20,903
2021		18,886
2022		17,245
2023		15,128
Thereafter		43,439
Total		$ 138,129
Lessee, Finance Leases, Sublease Rentals [Member]
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
Finance lease	11,257
Lessee, Operating Leases, Sublease Rentals [Member]
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2019 remaining	6,033
2020	23,454
2021	21,352
2022	19,579
2023	17,436
2024	12,255
Thereafter	36,572
Total	$ 136,681