Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net interest income	$ 75,852	$ 72,287	$ 227,133	$ 207,982
Noninterest income	34,575	35,627	101,802	101,705
Income before taxes	25,604	42,965	79,160	127,807
Total Assets	9,618,868		9,618,868		$ 8,565,758
Operating Segments [Member] | Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	20,476	21,955	64,970	64,746
Noninterest income	4,735	4,862	14,006	13,706
Income before taxes	6,669	15,670	20,695	45,905
Total Assets	2,952,325		2,952,325		2,806,021
Operating Segments [Member] | Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	43,369	44,707	131,784	132,889
Noninterest income	15,149	16,823	44,843	47,951
Income before taxes	18,257	29,710	58,225	87,796
Total Assets	5,718,312		5,718,312		4,998,247
Operating Segments [Member] | Pegasus Bank [Member]
Segment Reporting Information [Line Items]
Net interest income	5,078	2,954	15,662	2,954
Noninterest income	379	109	631	109
Income before taxes	1,429	1,404	4,372	1,404
Total Assets	761,505		761,505		738,351
Operating Segments [Member] | Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income	6,816	1,654	14,304	4,236
Noninterest income	10,882	10,916	31,100	30,894
Income before taxes	3,819	6,239	17,364	16,310
Total Assets	809,354		809,354		102,442
Operating Segments [Member] | Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income	(104)	1,017	196	3,157
Noninterest income	25,969	39,640	79,226	113,078
Income before taxes	17,158	25,882	44,793	78,495
Total Assets	487,192		487,192		950,920
Eliminations [Member]
Segment Reporting Information [Line Items]
Net interest income	217		217
Noninterest income	(22,539)	(36,723)	(68,004)	(104,033)
Income before taxes	(21,728)	$ (35,940)	(66,289)	$ (102,103)
Total Assets	$ (1,109,820)		$ (1,109,820)		$ (1,030,223)