Goodwill and Intangible Assets - Finite-lived Intangible Assets Roll Forward (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Finite-lived Intangible Assets, Gross [Roll Forward]
Intangible assets, January 1			$ 35,240	$ 35,240	$ 35,240
Additions			0		0
Total intangible assets, end of period	$ 35,240		35,240		35,240
Accumulated amortization, January 1
Accumulated amortization, January 1			(27,345)	(23,956)	(23,956)
Current year amortization	(658)	$ (847)	(1,318)	$ (1,694)	(3,389)
Total accumulated amortization	(28,663)		(28,663)		(27,345)
Net intangible assets, end of period	$ 6,577		$ 6,577		$ 7,895