Retirement Savings Plan (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Matching contributions	$ 2.4	$ 2.1	$ 2.8
First 3.0% [Member]
Defined Benefit Plan Disclosure [Line Items]
Company matching contribution percentage	100.00%
Percentage of employee's gross pay matched	3.00%
Next 2.0% [Member]
Defined Benefit Plan Disclosure [Line Items]
Company matching contribution percentage	50.00%
Percentage of employee's gross pay matched	2.00%