Employee Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 14, 2012
Employee Benefit Plans
Maximum contribution by employee (as a percent)	50.00%
Percentage of employer contribution of first 6 percent of covered compensation	50.00%
Maximum employee contribution matched by employer as a percentage of covered compensation	6.00%
Profit sharing and matching contribution expense	$ 23.2	$ 22.0	$ 20.4
Percentage of incentive compensation	100.00%
Net deferred compensation expense	0.7	1.0	0.7
Supplemental Executive Retirement Plan ("SERP")
Supplemental Executive Retirement Plan ("SERP"):
Number of executives (in persons)	1
Deferred compensation stock fund in equity				8.3
Pension expense from conversion of fully vested interest into the deferred compensation stock fund in equity			$ 1.7