Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 306,668	$ 281,921	$ 260,476
Provision for credit losses	62,648	8,287	3,802
Noninterest income	137,222	137,229	125,199
Depreciation and amortization	18,424	15,989	13,546
Other expenses	239,306	225,312	208,575
Income before taxes	123,512	169,562	159,752
Total assets	9,212,357	8,565,758	7,574,258
Capital expenditures	66,446	27,054	51,863
Operating Segments [Member] | Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	85,464	86,511	84,043
Provision for credit losses	30,202	2,143	79
Noninterest income	18,664	18,608	16,625
Depreciation and amortization	2,639	2,463	2,364
Other expenses	36,746	37,549	36,873
Income before taxes	34,541	62,964	61,352
Total assets	2,729,886	2,806,021	2,743,876
Capital expenditures	1,087	4,349	3,003
Operating Segments [Member] | Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	175,757	177,330	170,096
Provision for credit losses	29,827	5,606	4,178
Noninterest income	60,386	64,485	60,004
Depreciation and amortization	10,603	10,218	9,092
Other expenses	111,341	109,044	106,674
Income before taxes	84,372	116,947	110,156
Total assets	5,527,611	4,998,247	4,892,946
Capital expenditures	9,946	11,219	21,393
Operating Segments [Member] | Pegasus Bank [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	21,360	8,657
Provision for credit losses	1,916	140
Noninterest income	1,071	483
Depreciation and amortization	760	274
Other expenses	13,831	4,939
Income before taxes	5,924	3,787
Total assets	919,572	738,351
Capital expenditures	1,775	83
Operating Segments [Member] | Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	23,500	5,763	5,341
Provision for credit losses	562	(69)	(466)
Noninterest income	41,549	40,270	37,743
Depreciation and amortization	500	603	588
Other expenses	44,918	25,408	24,895
Income before taxes	19,069	20,091	18,067
Total assets	137,122	102,442	84,706
Capital expenditures	450	1,220	1,035
Operating Segments [Member] | Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	79	3,660	996
Provision for credit losses	141	467	11
Noninterest income	118,491	152,320	137,364
Depreciation and amortization	3,922	2,431	1,502
Other expenses	33,588	50,941	42,319
Income before taxes	80,919	102,141	94,528
Total assets	1,073,507	950,920	861,782
Capital expenditures	53,188	10,183	26,432
Eliminations [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	508
Noninterest income	(102,939)	(138,937)	(126,537)
Other expenses	(1,118)	(2,569)	(2,186)
Income before taxes	(101,313)	(136,368)	(124,351)
Total assets	$ (1,175,341)	$ (1,030,223)	$ (1,009,052)