Income Taxes - Summary of Activity Related to Uncertain Tax Positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of activity related to uncertain tax positions:
Balance at January 1,	$ 2,594	$ 3,561	$ 2,644
Additions Based on Tax Positions Related to the Current Year	456	258	331
Additions for Tax Positions of Prior Years	232	293	1,176
Prior Year Reductions	(236)	(776)	(1)
Statute Expirations	(346)	(609)	(589)
Settlements	(431)	(133)	0
Balance at December 31,	$ 2,269	$ 2,594	$ 3,561