Deferred Compensation Plans - Summary of Changes in Deferred Compensation Plan Liability (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Postemployment Benefits [Roll Forward]
Balance, beginning of year	$ 2,503	$ 2,080	$ 1,226
Deferrals, dividends, and changes in fair value recorded as an expense	64	444	936
Deferred compensation payments	(159)	(21)	(82)
Balance, end of year	$ 2,408	$ 2,503	$ 2,080