Income Taxes (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Tax Cuts and Jobs Act of 2017, income tax expense	$ 47,200
Decrease in valuation allowance	6,200	$ 2,100
Tax Cuts and Jobs Act of 2017, income tax expense	608
Deferred tax assets expected to be realized	165,800
Valuation allowance	3,431	9,658
Deferred tax assets, not subject to expiration	108,900
Tax credit carryforward, amount	6,200	2,100
Unrecognized tax benefits, income tax penalties and interest accrued	105	38	$ 96
Unrecognized tax benefits that would impact effective tax rate	12,300	9,900	$ 8,300
Unrecognized tax benefits, income tax penalties and interest accrued that would impact effective tax rate	76	$ 25
Approximate range of uncertain income tax positions expected to be settled or resolved during the next 12 months, minimum	17
Period through 2018
Income Tax Contingency [Line Items]
Valuation allowance	3,400
Period through 2035
Income Tax Contingency [Line Items]
Deferred tax assets, subject to expiration	41,100
Federal and State | Period through 2027
Income Tax Contingency [Line Items]
Tax credit carryforward, amount	$ 19,200