Stockholders' Equity - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Stockholders Equity [Line Items]
Value of shares that have been repurchased and retired during the period	$ 28,758,000
Stock Repurchase Plan
Stockholders Equity [Line Items]
Board of Directors authorized stock repurchase program	250,000,000
Stock repurchase remaining authorized amount	28,800,000	50,000,000
Number of shares that have been repurchased and retired during the period	826,800	1,681,029
Average price per share	$ 34.78	$ 29.76
Value of shares that have been repurchased and retired during the period	$ 171,200,000
Stock repurchase program, period	2 years