Employee Benefit Plans (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
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	$ 6.3	$ 5.4	$ 12.3	$ 10.7
Percentage of incentive compensation	100.00%		100.00%
Net deferred compensation expense	$ 0.5	$ 0.4	$ 0.4	$ 0.5