Stockholders' Equity - Additional Information (Detail) (USD $)	1 Months Ended		12 Months Ended
	Dec. 03, 2012	Oct. 16, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Shareholders Equity [Line Items]
Special dividend, per outstanding common share		$ 2.50
Special dividend	$ 486,141,000
Special dividends declared date			Oct. 16, 2012
Special dividends record date			Nov. 16, 2012
Repurchase of aggregate common shares			(250,000,000)
Shares repurchased			3,867,550	0	0
Maximum
Shareholders Equity [Line Items]
Share buyback program, authorization		$ 1,000,000,000