Stock-Based Compensation - Schedule of Nonvested Stock Option Outstanding (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shares
Nonvested at beginning of period (in shares)	140,076
Granted (in shares)	150,326
Vested (in shares)	(48,244)
Forfeited (in shares)	0
Nonvested at end of period (in shares)	242,158	140,076
Weighted- Average Exercise Price
Nonvested at beginning of period (in dollars per share)	$ 43.91
Vested (in dollars per share)	42.32
Granted (in dollars per share)	34.93
Forfeited (in dollars per share)	0
Nonvested at end of period (in dollars per share)	38.66	$ 43.91
Weighted- Average Grant Date Fair Value
Nonvested at beginning of period (in dollars per share)	10.53
Vested (in dollars per share)	10.27
Granted (in dollars per share)	7.19	10.26	$ 11.62
Forfeited (in dollars per share)	0
Nonvested at end of period (in dollars per share)	$ 8.51	$ 10.53