Equity - Additional Information (Detail) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Stockholders Equity Note Disclosure [Line Items]
Common stock, shares authorized	60,000,000			60,000,000	60,000,000
Common stock, shares issued	36,395,970			36,395,970	35,132,365
Common stock, shares outstanding	35,243,709			35,243,709	34,282,244
Treasury stock, shares	1,152,261			1,152,261	850,121
Treasury stock, cost	$ 6,455,000			$ 6,455,000	$ 5,017,000
Dividends payable, amount per share	$ 0.05	$ 0.05	$ 0.05	$ 0.05
Aggregate amount dividends paid				$ 5,200,000