Investments - Additional Information (Detail) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2012 Year	Dec. 31, 2011 Year
Schedule of Available-for-sale Securities [Line Items]
Investments, maximum maturity period, years	5	5
Unrealized gains, net of unrealized losses, on the investments in the bond portfolio	$ 1,171,000	$ 786,000