Earnings Per Share (Earnings Per Share) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net income	$ 27,994	$ 34,453	$ 21,935	$ 18,477	$ 19,881	$ 15,902	$ 21,383	$ 20,750	$ 102,859	$ 77,916	$ 55,789
Denominator:
Weighted average shares of common stock outstanding									11,771	11,771	11,947
Effect of dilutive common stock equivalents									79	346	132
Weighted average shares of common stock outstanding									11,850	12,117	12,079
Basic earnings per share
Earnings per share - basic	$ 2.38	$ 2.93	$ 1.86	$ 1.57	$ 1.71	$ 1.36	$ 1.80	$ 1.75	$ 8.74	$ 6.62	$ 4.67
Diluted earnings per share
Earnings per share - diluted	$ 2.36	$ 2.91	$ 1.86	$ 1.56	$ 1.66	$ 1.32	$ 1.75	$ 1.70	$ 8.68	$ 6.43	$ 4.62