Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Schedule of Reconciliation of Level 3 Investments Available-for-Sale Securities (Detail)

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Fair Value Measurements - Schedule of Reconciliation of Level 3 Investments Available-for-Sale Securities (Detail) (USD $)
6 Months Ended
Jun. 30, 2014
Fair Value Disclosures [Abstract]  
Balance, beginning of period $ 3,213,000
Transfers to / purchases of available-for-sale debt securities 83,500,000
Sale of available-for-sale debt securities (20,700,000)
Unrealized gain on debt securities transferred to available for sale 5,000,000
Unrealized (loss) on debt securities holdings (200,000)
Balance, end of period $ 67,640,000