Common and Preferred Stock - Additional Information (Detail) (USD $)	1 Months Ended		6 Months Ended
	Dec. 31, 2011	Apr. 30, 2008	Jun. 30, 2012
Stockholders Equity Note [Line Items]
Increase in share repurchase authorized amount	$ 50,000,000
Share repurchase authorized amount	125,000,000	75,000,000
Purchase of common stock (in shares)			865,151
Purchase of common stock			$ 36,042,000
Common stock, shares authorized	150,000,000		150,000,000
Common stock, par value	$ 0.01		$ 0.01
Preferred stock, shares authorized	5,000,000		5,000,000
Preferred stock, par value	$ 0.01		$ 0.01
Preferred stock, shares issued