Income Taxes Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Abstract]
Unrecognized tax benefits, beginning of period	$ 57,626	$ 54,880	$ 28,146
Gross increase to positions in prior years	3,367	1,164	6,461
Gross decrease to positions in prior years	(5,559)	(612)	(2,512)
Gross increases to current period tax positions	6,453	5,071	25,741
Audit settlements	(5,169)	(1,116)	0
Decrease related to lapsing of statute of limitations	(3,445)	(860)	(908)
Effect of change in exchange rates	3,429	(901)	(2,048)
Unrecognized tax benefits, end of period	56,702	57,626	54,880
The amount of unrecognized tax benefits that, if recognized, would affect our effective tax rate	55,312	56,411	53,602
Net interest and penalties expense (benefit)	(543)	193	$ 880
Accrued interest	2,706	2,473
Accrued penalties	$ 2,426	$ 2,329