Goodwill and Intangible Assets - Finite-lived Intangible Assets Roll Forward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018
Finite-lived Intangible Assets, Gross [Roll Forward]
Intangible assets, January 1	$ 35,240	$ 34,362
Additions	0	878
Total intangible assets, end of year	35,240	35,240
Accumulated Amortization [Roll Forward]
Accumulated amortization, January 1	(23,956)	(19,220)
Current year amortization	(3,389)	(4,736)
Total accumulated amortization	(27,345)	(23,956)
Net intangible assets, end of year	$ 7,895	$ 11,284	$ 7,900