Fair Value Measurement and Fair Value of Financial Instruments - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2012
Percentage of weighted average return on capital	16.20%
Weighted average percentage of probability default	0.60%
Weighted average percentage of loss severity	35.70%
Minimum [Member]
Percentage of return on capital	15.00%
Percentage of probability of default	0.03%
Percentage of loss severity	10.00%
Maximum [Member]
Percentage of return on capital	17.00%
Percentage of probability of default	8.00%
Percentage of loss severity	60.00%