Income Tax (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income Tax [Abstract]
Income tax expense	$ 2,067	$ 2,663	$ 4,105	$ 5,284
Statutory federal income tax rate			21.00%		35.00%
Decrease in income tax expense	(100)	$ (100)	$ (300)	$ (200)
Gross unrecognized tax benefits	$ 700		$ 700		$ 700

Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to excess tax benefit for share-based compensation cost.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of unrecognized tax benefits.

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