Shareholders' Equity - Reconciliation of Outstanding Balance of Stock Options (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options, Outstanding at beginning	558	513
Options, Granted	105	100
Options, Exercised	(358)	(55)
Options, Forfeited or expired	0	0
Options, Outstanding at ending	305	558
Options, Exercisable at ending	117
Options, Unvested at ending	188
Weighted Average Exercise Price, Outstanding at beginning	$ 31.22	$ 28.52
Weighted Average Exercise Price, Granted	15.36	39.54
Weighted Average Exercise Price, Exercised	29.36	21.26
Weighted Average Exercise Price, Forfeited or expired	0	0
Weighted Average Exercise Price, Outstanding at ending	27.94	31.22
Weighted Average Exercise Price, Exercisable at ending	33.12
Weighted Average Exercise Price, Unvested at ending	24.73
Weighted Average Grant Date Fair Value, Outstanding at beginning	14.03	13.10
Weighted Average Grant Date Fair Value, Granted	7.36	16.40
Weighted Average Grant Date Fair Value, Exercised	13.24	9.76
Weighted Average Grant Date Fair Value, Forfeited or expired	0	0
Weighted Average Grant Date Fair Value, Outstanding at ending	$ 12.65	$ 14.03
Aggregate Intrinsic Value, Outstanding	$ 5,886
Aggregate Intrinsic Value, Exercisable	1,647
Aggregate Intrinsic Value, Unvested	$ 4,239