Fair Value - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2013
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Period of Investment	2 years
Minimum [Member] | Discounted Cash Flow Valuation Technique [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	3.15%
Minimum [Member] | Sales Comparison Valuation Technique [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	10.00%
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Period of Investment	5 years
Maximum [Member] | Discounted Cash Flow Valuation Technique [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	8.00%
Maximum [Member] | Sales Comparison Valuation Technique [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Discount rate	25.00%