Fair Value Measurements - Changes in Level 3 Assets Measured at Estimated Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Balance at the beginning of the year	$ 21,385	$ 21,124
Purchases	157	1,096
Settlements	(212)	(191)
Sales		(429)
Losses included in earnings		(111)
Total unrealized losses	(676)	(104)
Balance at the end of the period	$ 20,654	$ 21,385