Common Stock and Treasury Stock - Additional Information (Detail) - USD ($)	9 Months Ended	36 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Feb. 28, 2014	Jul. 31, 2013	Sep. 13, 2012	Feb. 29, 2012	Dec. 31, 2011
Maximum stock authorized to purchase under stock repurchase program						$ 262,100,000	$ 210,000,000
Increase in maximum stock authorized to purchase under stock repurchase program			$ 100,000,000	$ 100,000,000		$ 52,100,000
Repurchase of common stock, shares	0	37,108,467
Repurchase of common stock, value		$ 395,800,000
Maximum [Member]
Maximum stock authorized to purchase under stock repurchase program					$ 113,000,000
Stock authorized to purchase under stock repurchase program, shares					7,500,000
Remaining value of shares authorized for purchase under the stock repurchase program	$ 138,300,000