Goodwill and Intangible Assets - Finite-lived Intangible Assets Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Finite-lived Intangible Assets, Gross [Roll Forward]
Intangible assets, January 1	$ 34,362	$ 34,362
Additions	878	0
Total intangible assets, end of year	35,240	34,362
Accumulated Amortization [Roll Forward]
Accumulated amortization, January 1	(19,220)	(11,933)
Current year amortization	(4,736)	(7,287)
Total accumulated amortization	(23,956)	(19,220)
Net intangible assets, end of year	$ 11,284	$ 15,142