Earnings Per Share - Calculation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Share Basic [Abstract]
Net income – basic	$ 34,014	$ 21,386	$ 17,890	$ 19,400	$ 18,806	$ 19,701	$ 16,956	$ 16,169	$ 92,690	$ 71,632	$ 46,231
Basic weighted-average common shares									19,248,657	19,208,978	19,165,489
Basic earnings per share	$ 1.77	$ 1.11	$ 0.93	$ 1.01	$ 0.98	$ 1.03	$ 0.88	$ 0.84	$ 4.82	$ 3.73	$ 2.41
Net income - diluted									$ 92,690	$ 71,632	$ 46,231
Weighted average common shares									19,248,657	19,208,978	19,165,489
Stock options and restricted stock									80,000	84,000	81,000
Diluted weighted average common shares									19,329,238	19,293,082	19,245,866
Diluted earnings per common share	$ 1.76	$ 1.11	$ 0.93	$ 1.01	$ 0.98	$ 1.02	$ 0.88	$ 0.84	$ 4.80	$ 3.71	$ 2.40