Subsequent Event - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended		1 Months Ended
	Dec. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Jan. 31, 2011 Common Shares [Member]	Jan. 24, 2011 Common Shares [Member]	Jan. 28, 2014 Subsequent Event [Member] Common Shares [Member]	Jan. 31, 2014 Subsequent Event [Member] Common Shares [Member]
Subsequent Event [Line Items]
Common stock, shares issued		116,494,000	115,259,000		19,000,000	9,775,000
Proceeds from sale of common stock	$ 219,783,000			$ 220,400,000		$ 117,200,000	$ 117,200,000
Legal, accounting fees, filing fees and other offering expenses				$ 600,000		$ 600,000	$ 600,000