Stockholders Equity - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended		1 Months Ended
	Feb. 29, 2012	Dec. 31, 2012	Dec. 31, 2011	Jan. 31, 2013 Common Stock Issued In Public Offering	Jul. 31, 2005 Rights	Jul. 13, 2005 Rights
Stockholders Equity [Line Items]
Preferred stock, shares authorized		5,000,000	5,000,000
Preferred stock, par value		$ 0.01	$ 0.01
Right to buy Series A Junior Preferred stock declared as dividend						0.001
Date on which rights expire						Jul. 13, 2015
Acquisition of outstanding common stock that trigger exercise of right					50.00%
Tender or exchange offer for outstanding common stock that trigger exercise of right					20.00%
Cash purchase price of Series A Junior Preferred stock						80.00
Common stocks issued through underwritten public offering	8,625,000			9,200,000
Underwritten public offering amount per share	$ 10.75			$ 20.13
Net proceeds from public issue, after deducting expenses	$ 86,800,000	$ 86,800,000		$ 173,600,000
Underwriting discounts and commissions and other estimated offering expenses	$ 5,900,000			$ 11,600,000