Fair Value Measurements - Change in Estimated Fair Value Calculated for Investment Valued on Recurring Basis Utilizing Level 3 Inputs (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($)
Fair Value Disclosures [Abstract]
Balance at the beginning of the period	$ 2,575
Credit gain on available-for-sale securities included in Other income (expense), net	12
Gain included in Other comprehensive income (loss)	42
Balance at the end of the period	$ 2,629