Fair Value Measurements - Changes in Level 3 Assets Measured at Estimated Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Balance at the beginning of the year	$ 12,714	$ 13,443
Transfers from level 2	1,643
Settlements	(1,473)	(695)
Total unrealized losses	(15)	(34)
Balance at the end of the period	$ 12,869	$ 12,714