Debt - Aggregate Required Principal Payments (Details) - Mortgages - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Amortization
2018, amortization	$ 2,749
2019, amortization	3,790
2020, amortization	3,938
2021, amortization	4,090
2022, amortization	5,628
Thereafter, amortization	41,744
Total, amortization	61,939
Maturities
2018, maturities	0
2019, maturities	250,000
2020, maturities	0
2021, maturities	0
2022, maturities	265,000
Thereafter, maturities	1,355,422
Total, maturities	1,870,422
Total long term debt
2018	2,749
2019	253,790
2020	3,938
2021	4,090
2022	270,628
Thereafter	1,397,166
Total	$ 1,932,361	$ 1,701,224