Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, beginning of year		$ 2,194	$ 1,970	$ 2,519
Additions for tax positions taken in prior years	$ 5,600	41	38	21
Reductions for tax positions taken in prior years		(4)	(5)	(523)
Additions for tax positions related to the current year		116	211	83
Lapses of statutes of limitations		(12)	(11)	(130)
Other		(5)	(9)	0
Unrecognized tax benefits, end of year	2,194	2,330	2,194	1,970
Unrecognized tax benefits that would impact effective tax rate, if recognized		2,100
Income tax penalties and interest expense		300	300	$ (1,900)
Cumulative liability for interest and penalties related to uncertain tax positions	$ 1,000	1,300	$ 1,000
Previously unrecognized tax benefit likely to be recognized within the next 12 months		$ 100