Income Tax Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Tax Contingency [Line Items]
Release of reserves for uncertain tax positions		$ 900
Change in income tax expense	$ 3,300
Effective income tax rate	15.00%	3.90%	14.60%	13.80%
Income tax expense	$ 4,006	$ 671	$ 6,885	$ 5,060