Goodwill and Intangible Assets - Finite-lived Intangible Assets Roll Forward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Finite-lived Intangible Assets, Gross [Roll Forward]
Intangible assets, January 1	$ 35,240	$ 34,362
Additions	0	0
Total intangible assets, end of period	35,240	34,362
Accumulated amortization, January 1
Accumulated amortization, January 1	(23,955)	(19,220)
Current year amortization	(847)	(1,270)
Total accumulated amortization	(24,802)	(20,490)
Net intangible assets, end of period	$ 10,438	$ 13,872