Loans and Other Real Estate - Company's Commercial Loan Portfolio (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 5,855,024	$ 5,140,940
Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,049,331	3,589,593
Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment [Line Items]
Total loans	751,936
Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	276,743	335,169
Total Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,078,010	4,356,696
Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Total loans	426,821	431,934
1 | Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
1 | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment [Line Items]
Total loans	325,510
1 | Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
1 | Total Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	325,510	898
1 | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Total loans		898
2 | Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
2 | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment [Line Items]
Total loans	16,344
2 | Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
2 | Total Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	16,344	17,988
2 | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Total loans		17,988
3 | Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	72,698	74,072
3 | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment [Line Items]
Total loans	26,492
3 | Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
3 | Total Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	99,190	113,184
3 | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Total loans		39,112
4 | Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	955,104	965,825
4 | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment [Line Items]
Total loans	91,708
4 | Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	18,901	17,941
4 | Total Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,065,713	1,091,142
4 | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Total loans		107,376
5 | Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,954,831	2,332,863
5 | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment [Line Items]
Total loans	205,623
5 | Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	221,750	307,824
5 | Total Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,382,204	2,856,662
5 | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Total loans		215,975
5W - Watch | Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	796,979	100,347
5W - Watch | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment [Line Items]
Total loans	51,092
5W - Watch | Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,924	6,959
5W - Watch | Total Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	869,995	137,498
5W - Watch | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Total loans		30,192
6 - Other assets especially mentioned | Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	147,407	55,438
6 - Other assets especially mentioned | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment [Line Items]
Total loans	22,476
6 - Other assets especially mentioned | Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,503	0
6 - Other assets especially mentioned | Total Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	182,386	66,766
6 - Other assets especially mentioned | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Total loans		11,328
7 - Substandard | Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	122,312	61,048
7 - Substandard | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,691
7 - Substandard | Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,665	2,445
7 - Substandard | Total Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	136,668	72,558
7 - Substandard | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Total loans		9,065
8 - Doubtful | Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
8 - Doubtful | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment [Line Items]
Total loans	0
8 - Doubtful | Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
8 - Doubtful | Total Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
8 - Doubtful | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Total loans		0
9 - Loss | Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
9 - Loss | Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment [Line Items]
Total loans	0
9 - Loss | Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
9 - Loss | Total Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 0	0
9 - Loss | Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Total loans		$ 0