Debt Obligations, Junior Subordinated Notes (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Debt Obligations
Gain on extinguishment of debt		$ 7,116
Debt carrying value	$ 139,760		$ 139,590
Weighted average note rate (as a percent)	3.74%		3.34%
Junior subordinated notes
Debt Obligations
Junior Subordinated, Face Value		20,900
Debt carrying value purchased		19,800
Gain on extinguishment of debt		7,100
Extinguishment of notes		$ 21,500
Debt carrying value	$ 139,800		$ 139,600
Deferred amount Due at maturity	12,400		12,500
Deferred fees expensed as interest expense	$ 2,200		$ 2,200
Weighted average note rate (as a percent)	5.16%		4.53%
Weighted average note rate including certain fees and costs (as a percent)	5.25%		4.63%