Fair Value Measurements - Changes in Assets Classified as Level 3 in Fair Value Hierarchy (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period							$ 300
Total gains included in other comprehensive income		[1]		[1]		[1]	44	[1]
Net purchases, sales, issuances and settlements
Transfers out of Level 3							(344)
Balance at end of period

[1] Changes in estimated fair value of available-for-sale investments are recorded in accumulated other comprehensive income (loss), while realized gains and losses from sales are recorded in security gains (losses), net in the Consolidated Statements of Comprehensive Income.