Condensed Quarterly Statements of Income (Unaudited) - Consolidated Selected Quarterly Statements of Income (Detail) - USD ($) $ / shares in Units, $ 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
Income Statement [Abstract]
Interest and dividend income	$ 130,478	$ 133,657	$ 134,694	$ 142,448	$ 128,309	$ 117,348	$ 119,543	$ 119,053	$ 541,277	$ 484,253
Interest expense	10,766	13,064	15,681	22,286	21,345	21,228	21,083	20,692	61,797	84,349
Net interest income	119,712	120,593	119,013	120,162	106,964	96,120	98,460	98,361	479,480	399,904
Provision for credit losses	(209)	16,288	61,841	29,821	1,824	4,121	2,747	2,507	107,741	11,198	$ 7,764
Net interest income after provision for credit losses	119,921	104,305	57,172	90,341	105,140	91,999	95,713	95,854	371,739	388,706
Non-interest income	32,014	33,825	31,561	26,518	30,318	26,715	28,247	27,116	123,917	112,396
Net securities gains	691	787	1,299	1,491	520	235	2,909	657	4,268	4,320
Non-interest expense	88,069	89,943	85,502	91,333	92,556	73,268	71,952	74,432	354,845	312,208	265,224
Income before provision for income taxes	64,557	48,974	4,530	27,017	43,422	45,681	54,917	49,195	145,079	193,214	174,524
Provision for income taxes	11,703	7,669	42	3,621	7,046	8,334	10,103	8,858	23,035	34,341	31,412
NET INCOME	52,854	41,305	4,488	23,396	$ 36,376	$ 37,347	$ 44,814	$ 40,337	122,044	158,873	143,112
Preferred stock dividends	2,644								2,644
NET INCOME AVAILABLE TO COMMON SHAREHOLDERS	$ 50,210	$ 41,305	$ 4,488	$ 23,396					$ 119,400	$ 158,873	$ 143,112
Earnings per common share—basic	$ 0.75	$ 0.61	$ 0.07	$ 0.34	$ 0.60	$ 0.68	$ 0.82	$ 0.74	$ 1.78	$ 2.83	$ 2.93
Earnings per common share—diluted	$ 0.75	$ 0.61	$ 0.07	$ 0.34	$ 0.60	$ 0.68	$ 0.82	$ 0.74	$ 1.77	$ 2.83	$ 2.92