Loans and Other Real Estate - Commercial Loan Portfolio (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 5,279,739	$ 5,097,820
Commercial, secured by real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,740,319	3,589,593
Commercial, secured by real estate | 1
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Commercial, secured by real estate | 2
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Commercial, secured by real estate | 3
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	73,368	74,072
Commercial, secured by real estate | 4
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	986,743	965,825
Commercial, secured by real estate | 5
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,329,762	2,332,863
Commercial, secured by real estate | 5W - Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	227,836	100,347
Commercial, secured by real estate | 6 - Other assets especially mentioned
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	59,250	55,438
Commercial, secured by real estate | 7 - Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	63,360	61,048
Commercial, secured by real estate | 8 - Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Commercial, secured by real estate | 9 - Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Commercial, industrial and other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	467,346	431,934
Commercial, industrial and other | 1
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	554	898
Commercial, industrial and other | 2
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	18,099	17,988
Commercial, industrial and other | 3
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	35,528	39,112
Commercial, industrial and other | 4
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	117,485	107,376
Commercial, industrial and other | 5
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	203,708	215,975
Commercial, industrial and other | 5W - Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	68,160	30,192
Commercial, industrial and other | 6 - Other assets especially mentioned
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	9,338	11,328
Commercial, industrial and other | 7 - Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	14,474	9,065
Commercial, industrial and other | 8 - Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Commercial, industrial and other | 9 - Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Real estate - construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	333,592	335,169
Real estate - construction | 1
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Real estate - construction | 2
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Real estate - construction | 3
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Real estate - construction | 4
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	17,899	17,941
Real estate - construction | 5
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	301,455	307,824
Real estate - construction | 5W - Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,050	6,959
Real estate - construction | 6 - Other assets especially mentioned
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	11,472	0
Real estate - construction | 7 - Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,716	2,445
Real estate - construction | 8 - Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Real estate - construction | 9 - Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Total Commercial Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	4,541,257	4,356,696
Total Commercial Loans | 1
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	554	898
Total Commercial Loans | 2
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	18,099	17,988
Total Commercial Loans | 3
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	108,896	113,184
Total Commercial Loans | 4
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,122,127	1,091,142
Total Commercial Loans | 5
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,834,925	2,856,662
Total Commercial Loans | 5W - Watch
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	297,046	137,498
Total Commercial Loans | 6 - Other assets especially mentioned
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	80,060	66,766
Total Commercial Loans | 7 - Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	79,550	72,558
Total Commercial Loans | 8 - Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0	0
Total Commercial Loans | 9 - Loss
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 0	$ 0