Summary of Quarterly Results of Operations (unaudited) - Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Loans:
Discount accretion	$ 1,780	$ 2,034	$ 2,566	$ 1,712	$ 1,960	$ 1,876	$ 2,587	$ 1,748
All other loan interest income	59,024	58,691	57,738	58,724	59,055	56,163	55,822	54,510
Total loan interest income	60,804	60,725	60,304	60,436	61,015	58,039	58,409	56,258	$ 242,269	$ 233,721	$ 223,750
Debt securities, dividends and interest bearing cash at banks	10,220	8,903	8,175	7,480	7,066	7,399	8,739	10,259
Total interest and dividend income	71,024	69,628	68,479	67,916	68,081	65,438	67,148	66,517	277,047	267,184	272,444
Interest expense	1,241	1,395	1,396	1,476	1,659	1,984	2,489	3,325	5,508	9,457	15,375
Net interest income	69,783	68,233	67,083	66,440	66,422	63,454	64,659	63,192	271,539	257,727	257,069
Provision for (benefit from) credit losses	980	(1,435)	(260)	(6,060)	4,850	7,649	22,244	8,070	(6,775)	42,813	(1,690)
Net interest income after provision for (benefit from) credit losses	68,803	69,668	67,343	72,500	61,572	55,805	42,415	55,122	278,314	214,914	258,759
Noninterest income	16,502	15,095	15,957	16,110	16,580	15,137	11,657	11,820	63,664	55,194	53,520
Total noninterest expense	46,679	45,807	44,171	41,618	45,745	46,714	45,550	44,749	178,275	182,758	185,457
Income before income taxes	38,626	38,956	39,129	46,992	32,407	24,228	8,522	22,193	163,703	87,350	126,822
Income tax expense	10,404	11,534	10,767	13,343	8,750	6,622	1,092	6,072	46,048	22,536	34,750
Net income	$ 28,222	$ 27,422	$ 28,362	$ 33,649	$ 23,657	$ 17,606	$ 7,430	$ 16,121	$ 117,655	$ 64,814	$ 92,072
Per common share:
Net income (diluted) (in USD per share)	$ 0.94	$ 0.92	$ 0.95	$ 1.13	$ 0.79	$ 0.59	$ 0.25	$ 0.53	$ 3.94	$ 2.16	$ 3.00
Dividends paid (in USD per share)	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.22	$ 0.22	$ 0.22	$ 0.22	$ 1.00	$ 0.88	$ 0.82