Employee Benefit Plans (Defined Contribution Plan) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Percentage of employer contribution as percentage of first three percentage of eligible compensation	100.00%
Percentage of eligible compensation contributed by employer	3.00%
Percentage of employer contribution as percentage of next two percentage of eligible compensation	50.00%
Percentage of eligible compensation contributed by each employee	2.00%
Total expense recorded for matching 401(k) contributions	$ 51.7	$ 46.8	$ 40.9