Fair Value Measurements - Change in Estimated Fair Values Calculated for Investment Valued on Recurring Basis Utilizing Level 3 Inputs (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($)
Fair Value Disclosures [Abstract]
Balance at the beginning of the period	$ 2,510
Credit gain on available-for-sale security included in Other income (expense), net	2
Gain included in Other comprehensive income	43
Balance at the end of the period	$ 2,555