Fair Value Measurement of Assets and Liabilities - Changes in Level 3 Assets Measured at Fair Value on Recurring Basis (Detail) (Available-for-sale Securities [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Mar. 31, 2014	Mar. 31, 2013
Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance, beginning of the period			$ 28,523	$ 71,674	$ 26,029	$ 79,112
Total net gains included in other comprehensive income for the period	341	218	563	11,657
Settlements	(669)	(1,119)	(3,385)	(5,120)
Balance, end of the period	$ 25,701	$ 78,211	$ 25,701	$ 78,211	$ 26,029	$ 79,112