Income Taxes - Unrecognized Tax Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Gross unrecognized tax benefits at beginning of year	$ 1,088	$ 2,665	$ 5,011
Increases in tax positions for prior years	130	16	22
Decreases in tax positions for prior years	(33)	(390)	(1,684)
Increases in tax positions for current years	182	0	336
Decreases in tax positions for current years	0	(54)	0
Decreases from lapse in statute of limitations	(255)	(1,149)	(1,020)
Gross unrecognized tax benefits at end of year	$ 1,112	$ 1,088	$ 2,665