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Employee Benefits - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Maximum percentage of a participant's eligible compensation that a participating may elect to contribute, on a tax-deferred annually to the plan (as a percent) 50.00%	80.00%
Percentage of matching contribution made by company, of first 6% of participating employees contributions (as a percent)	50.00%
Percentage of participating employees contribution, matched 100% (as a percent)	6.00%
Employer contribution	$ 9.0	$ 8.5	$ 7.9
Deferred gains or (losses) of investment	$ (0.7)	$ 3.7	$ 8.2