Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	$ 0	$ 0	$ 0	$ 0	$ 0
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	54,240		47,011
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | U.S. government and government agency obligations [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	2,864		22,890
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Mortgage-backed securities [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	5,106		8,216
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Asset-backed securities [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	6,000		3,537
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | U.S. government and government agency obligations [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Mortgage-backed securities [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Asset-backed securities [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	54,240		47,011
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | U.S. government and government agency obligations [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	2,864		22,890
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Mortgage-backed securities [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	5,106		8,216
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Significant Other Observable Inputs (Level 2) [Member] | Asset-backed securities [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	6,000		3,537
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | U.S. government and government agency obligations [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Mortgage-backed securities [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Significant Unobservable Inputs (Level 3) [Member] | Asset-backed securities [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Cash equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	36,861		4,402
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Cash equivalents [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Cash equivalents [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	36,861		4,402
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Cash equivalents [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Municipal bonds [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	1,564		3,059
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Municipal bonds [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Municipal bonds [Member] | Significant Other Observable Inputs (Level 2) [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	1,564		3,059
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Municipal bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Corporate bonds [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	1,845		4,907
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Corporate bonds [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Corporate bonds [Member] | Significant Other Observable Inputs (Level 2) [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value	1,845		4,907
Assets and Liabilities Measured at Fair Value on a Recurring Basis [Member] | Corporate bonds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Available-for-sale debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total assets measured at fair value