Debt - Maturities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Debt maturities
2019	$ 19,000
2020	150,000
2021	100,000
Thereafter	525,000
Total principal outstanding	794,000	$ 694,000
Unamortized deferred financing costs	(5,213)	(3,550)
Total debt	$ 788,787	$ 690,450