Retirement Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Defined contribution 401(k) plan, employer matching contribution, percent of match	50.00%
Defined contribution 401(k) plan, employee contributions subject to employer match (percent)	4.00%
401(k) plan, expense for matching contributions	$ 3.2	$ 3.0	$ 2.9