Stock-Based Compensation - Schedule of Nonvested Stock Option Outstanding (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Nonvested at beginning of period (in shares)	389,134
Granted (in shares)	72,521
Vested (in shares)	330,012
Forfeited (in shares)	7,295
Nonvested at end of period (in shares)	124,348	389,134
Weighted- Average Exercise Price
Nonvested at beginning of period (in dollars per share)	$ 23.25
Granted (in dollars per share)	48.33
Vested (in dollars per share)	20.59
Forfeited (in dollars per share)	47.01
Nonvested at end of period (in dollars per share)	42.76	$ 23.25
Weighted- Average Grant Date Fair Value
Nonvested at beginning of period (in dollars per share)	6.24
Granted (in dollars per share)	11.62	11.50	$ 7.84
Vested (in dollars per share)	5.69
Forfeited (in dollars per share)	11.38
Nonvested at end of period (in dollars per share)	$ 10.38	$ 6.24