Stock Repurchase Plan - Additional Information (Detail) (USD $)	1 Months Ended	6 Months Ended	12 Months Ended	90 Months Ended		1 Months Ended	6 Months Ended
	Feb. 29, 2012	Jun. 30, 2013	Dec. 31, 2011	Jun. 30, 2013	Jul. 31, 2013 Subsequent Event	Sep. 13, 2012 Maximum	Jun. 30, 2013 Maximum
Maximum stock authorized to purchase under stock repurchase program	$ 262,100,000		$ 210,000,000			$ 113,000,000
Increase in maximum stock authorized to purchase under stock repurchase program	52,100,000				100,000,000
Stock authorized to purchase under stock repurchase program, shares						2,500,000
Repurchase of common stock, shares		357,944		9,877,816
Repurchase of common stock, value		16,009,000		260,900,000
Remaining authorized shares for repurchase under the stock repurchase program							1,400,000
Remaining value of shares authorized for purchase under the stock repurchase program							$ 67,300,000