Share Based Award Options exercised data (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Intrinsic value of options exercised	$ 71,283	$ 25,065	$ 28,071
Cash received from exercise of stock options	32,003	17,346	15,042
Tax benefit from stock option exercises	$ 20,004	$ 7,556	$ 9,330