Stockholders' Equity - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended			3 Months Ended		9 Months Ended
	Feb. 27, 2012	Oct. 31, 2011	Oct. 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of Common Stock, shares	12,000,000
Sale of Common Stock, par value	$ 0.01			$ 0.01		$ 0.01		$ 0.01
Sale of Common Stock, Price Per Share	$ 30.83
Proceeds from sale of Common Stock						$ 369,584
Underwriting discounts and estimated transaction expenses payable						376
Weighted average grant date fair value per share						$ 31.50
Repurchase of common stock, maximum value						1,200,000
Repurchase of common stock						619,447	2,823,235
Payments for repurchase of common stock						18,597	85,068
Remaining value of common stock authorized under repurchase program						415,960
Cash dividend per share			$ 0.075	$ 0.090	$ 0.075	$ 0.270	$ 0.225
Cash dividend per common share, increase		$ 0.015
Cash dividends on common stock						32,182	25,497
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash dividend per share		$ 0.075
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash dividend per share		$ 0.09
Restricted stock units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock based compensation expense from restricted stock units						$ 13,435	$ 8,873