Stock-Based Compensation - Summary of Options Including Non-Plan Stock Options (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Stock Options:
Outstanding at beginning of year (in shares)	1,339,106
Granted (in shares)	72,521
Exercised (in shares)	613,588
Forfeited (in shares)	7,295
Outstanding at end of year (in shares)	790,744	1,339,106
Nonvested at end of year (in shares)	124,348	389,134
Exercisable at end of year (in shares)	666,396
Weighted- Average Exercise Price
Outstanding at beginning of year (in dollars per share)	$ 19.08
Granted (in dollars per share)	48.33
Exercised (in dollars per share)	17.63
Forfeited (in dollars per share)	47.01
Outstanding at end of year (in dollars per share)	22.48	$ 19.08
Nonvested at end of year (in dollars per share)	42.76	$ 23.25
Exercisable at end of year (in dollars per share)	$ 18.69
Weighted- Average Remaining Contractual Term (Year)
Outstanding at end of year	2 years 2 months 6 days	2 years 6 months 21 days
Nonvested at end of year	5 years 8 months 10 days
Exercisable at end of year	1 year 6 months 29 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value [Roll Forward]
Outstanding at end of year	$ 13,235	$ 38,525
Nonvested at end of year	603
Exercisable at end of year	$ 12,923