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
	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
Total net gains for the period included in other comprehensive income	48	8,033
Settlements	(1,660)	(1,787)
Balance, end of the period	$ 26,911	$ 77,920