Income Taxes - Net Deferred Income Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Net deferred income tax liabilities
Deferred income tax assets	$ 65,690	$ 77,270
Deferred income tax liabilities	(33,748)	(42,576)
Valuation allowance	(17,823)	(17,414)
Net deferred income tax assets	$ 14,119	$ 17,280