Accumulated Other Comprehensive Income (Loss) - Schedule of Reclassifications Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other income	$ 1,261	$ 1,002	$ 3,297	$ 1,780
Benefit from income taxes	(330)	(66)	(650)	(264)
Net of tax		(17)		(32)
Accumulated Net Unrealized Investment Gain (Loss) Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Other income		(17)		(32)
Benefit from income taxes	$ 0	$ 0	$ 0	$ 0