Income Taxes Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Interest accrued	$ 200	$ 800
Penalties expense	1,100	400
Decrease in unrecognized tax benefits is reasonably possible	100
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	8,600	9,207	$ 7,518
Increases in uncertain tax benefits as a result of tax positions taken in a prior year	1,013	287
Increases in uncertain tax benefits as a result of tax positions taken in the current year	545	1,367	1,845
Decreases in uncertain tax benefits from a lapse of applicable statute of limitations	(739)	(233)	(156)
Decreases in uncertain tax benefits as a result of tax positions taken in a prior year	(93)	(2,028)
Ending balance	$ 9,326	$ 8,600	$ 9,207