Reconciliation of Total Amounts of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Beginning balance of unrecognized tax benefits	$ 4,962	$ 5,490	$ 6,274
Additions based on tax positions related to the current year	991	561	752
Additions for tax positions of prior years	496	88	78
Reductions to tax positions of prior years	(28)	(45)	(626)
Reductions to tax positions resulting from a lapse of the applicable statute of limitations	(1,577)	(842)	(226)
Settlements with tax authorities	(755)	(290)	(762)
Ending balance of unrecognized tax benefits	$ 4,089	$ 4,962	$ 5,490