Income Taxes - Income Tax Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current expense (benefit)
United States	$ (906)	$ 3,702	$ 5,455
Foreign	28,109	28,156	20,351
Current income tax expense (benefit)	27,203	31,858	25,806
Deferred expense (benefit)
United States	27,770	9,489	(152)
Foreign	83	(1,640)	2,340
Deferred Income Tax Expense (Benefit), Total	27,853	7,849	2,188
Income tax expense as reported	$ 55,056	$ 39,707	$ 27,994