Stockholders' Equity (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Repurchase Program
Shares Repurchased Under Board Authorization	2,671,637	2,005,200	2,470,000
Total cost (in dollars)	$ 48.2	$ 28.2	$ 23.5
Average share price (in dollars per share)	$ 18.03	$ 14.05	$ 9.50
Shares repurchased to satisfy minimum statutory withholding tax upon the net settlement of equity awards	367,367	352,051	270,467
October 2011
Stock Repurchase Program
Amount Authorized by Board (in shares)	4,000,000
Total Shares Purchased	4,000,000
Shares Repurchased Under Board Authorization		1,500,000	2,500,000
May 2013
Stock Repurchase Program
Amount Authorized by Board (in shares)	4,000,000
Total Shares Purchased	3,200,000
Shares Remaining Under Board Authorization	800,000
Shares Repurchased Under Board Authorization	2,700,000	500,000
October 2014
Stock Repurchase Program
Amount Authorized by Board (in shares)	4,000,000
Shares Remaining Under Board Authorization	4,000,000