Goodwill and Intangible Assets - Finite-lived Intangible Assets Roll Forward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2019
Finite-lived Intangible Assets, Gross [Roll Forward]
Intangible assets, January 1	$ 35,240	$ 35,240
Additions	0	0
Total intangible assets, end of period	35,240	35,240
Accumulated amortization, January 1
Accumulated amortization, January 1	(27,345)	(23,956)
Current year amortization	(658)	(3,389)
Total accumulated amortization	(28,003)	(27,345)
Net intangible assets, end of period	$ 7,237	$ 7,895	$ 7,237