Income Taxes Tax benefit from exercise of stock options (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options	$ 20,004	$ 7,556	$ 9,330
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	$ 7,247	$ 5,682	$ 4,922