Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Tax Contingency [Line Items]
Change in income tax expense	$ 1,600
Effective income tax rate	15.00%	11.00%	14.70%	12.80%
Income tax expense	$ 3,716	$ 2,081	$ 10,601	$ 7,141