Debt and Preferred Stock - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Components of interest expense
Contractual coupon interest	$ 1,984	$ 1,723	$ 5,694	$ 4,555
Amortization of discount and deferred financing	278	367	842	871
Total interest expense	$ 2,262	$ 2,090	$ 6,536	$ 5,426