Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Unrecognized tax benefits	$ 28,421	$ 28,004	$ 27,688
Tax benefits which would favorable affect effective tax rate	22,400
Anticipated uncertain tax position adjustment	7,100
Income tax penalties and interest accrued	4,500	3,500
Interest on income taxes expense	800	300	$ 1,200
Income taxes receivable	42,400	$ 13,000
Favorably affect the effective tax rate [Member]
Income Tax Contingency [Line Items]
Anticipated uncertain tax position adjustment	$ 5,600