Fair Value Measurements - Change in Estimated Fair Values Calculated for Assets Valued on Recurring Basis Utilizing Level 3 Inputs (Detail) (Recurring [Member], Significant Unobservable Inputs (Level 3) [Member], Failed Auction Securities [Member], USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Failed Auction Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at the beginning of the period	$ 4,979
Redemptions, at par	(100)
Credit loss on available-for-sale securities included in Other income (expense), net	(79)
Unrealized gain included in Other comprehensive income (loss)	117
Balance at the end of the period	$ 4,917