Stock-Based Compensation - SAR Activity (Detail) - Stock Appreciation Rights [Member] - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Stock Appreciation Rights Activity [Line Items]
SARs Outstanding, Beginning Balance	278,116	275,450	524,154
Granted, SARs	21,260	37,478
Exercised, SARs	(60,900)	(34,812)	(248,704)
Canceled, SARs	0	0	0
Shares Outstanding, SARs, Ending Balance	238,476	278,116	275,450
Outstanding, Weighted Average Grant Price Per Share, Beginning Balance	$ 13.45	$ 9.79	$ 6.57
Vested, SARs	192,232
Granted, Weighted Average Grant Price Per Share	$ 56.59	35.38
Exercisable, SARs	192,232
Exercised, Weighted Average Grant Price Per Share	$ 5.27	8.07	5.55
Canceled, Weighted Average Grant Price Per Share	0	0	0
Outstanding, Weighted Average Grant Price Per Share, Ending Balance	19.26	$ 13.45	$ 9.79
Vested, Weighted Average Grant Price Per Share	13.08
Exercisable, Weighted Average Grant Price Per Share	$ 13.08
Weighted Average Remaining Contractual Life, Outstanding	5 years 3 months 18 days
Weighted Average Remaining Contractual Life, Vested	4 years 6 months
Weighted Average Remaining Contractual Life, Exercisable	4 years 6 months
Aggregate Intrinsic Value, Outstanding	$ 9,562,603
Aggregate Intrinsic Value, Vested	8,896,335
Aggregate Intrinsic Value, Exercisable	$ 8,896,335