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Financial Instruments - Quantitative Information about Level 3 Fair Value Measurements (Parenthetical) (Detail) (Level 3 [Member])	Mar. 31, 2014
Auction Rate Preferred Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
U.S. Treasury rate	1.29%
Municipal Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value assumption discount rate range of spread rate on treasury securities	175.00%
U.S. Treasury rate	1.51%
Student Loan Auction Rate Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value assumption discount rate range of spread rate on treasury securities	1.20%
U.S. Treasury rate	2.30%
Minimum [Member] \| Auction Rate Preferred Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value assumption discount rate range of spread rate on treasury securities	110.00%
Maximum [Member] \| Auction Rate Preferred Securities [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value assumption discount rate range of spread rate on treasury securities	150.00%