Intangible Assets - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense	$ 1,153	$ 1,529	$ 1,061
Expected amortization expense for year one	1,153
Expected amortization expense for year two	1,153
Expected amortization expense for year three	1,153
Expected amortization expense for year four	$ 600