Short Term Debt - Additional Information (Detail) (USD $)	1 Months Ended	6 Months Ended
	Mar. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Short-term Debt [Line Items]
Short-term debt outstanding		$ 40,891,000	$ 44,137,000
Short-term debt, maturity date		2011-07
Average balance of short-term debt		25,000,000
Weighted average interest rate		1.52%
Repayment short-term debt	$ 44,000,000	$ 3,246,000