Loans and Other Real Estate - Company's Commercial Loan Portfolio (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 5,769,127	$ 5,140,940
Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,961,476	3,589,593
Commercial, secured by real estate | 1
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial, secured by real estate | 2
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial, secured by real estate | 3
Financing Receivable, Recorded Investment [Line Items]
Total loans	70,963	74,072
Commercial, secured by real estate | 4
Financing Receivable, Recorded Investment [Line Items]
Total loans	903,575	965,825
Commercial, secured by real estate | 5
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,969,384	2,332,863
Commercial, secured by real estate | 5W - Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans	834,041	100,347
Commercial, secured by real estate | 6 - Other assets especially mentioned
Financing Receivable, Recorded Investment [Line Items]
Total loans	96,908	55,438
Commercial, secured by real estate | 7 - Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	86,605	61,048
Commercial, secured by real estate | 8 - Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial, secured by real estate | 9 - Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial, Industrial and Other (including PPP)
Financing Receivable, Recorded Investment [Line Items]
Total loans	728,238
Commercial, Industrial and Other (including PPP) | 1
Financing Receivable, Recorded Investment [Line Items]
Total loans	326,662
Commercial, Industrial and Other (including PPP) | 2
Financing Receivable, Recorded Investment [Line Items]
Total loans	16,730
Commercial, Industrial and Other (including PPP) | 3
Financing Receivable, Recorded Investment [Line Items]
Total loans	36,872
Commercial, Industrial and Other (including PPP) | 4
Financing Receivable, Recorded Investment [Line Items]
Total loans	90,751
Commercial, Industrial and Other (including PPP) | 5
Financing Receivable, Recorded Investment [Line Items]
Total loans	167,781
Commercial, Industrial and Other (including PPP) | 5W - Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans	61,609
Commercial, Industrial and Other (including PPP) | 6 - Other assets especially mentioned
Financing Receivable, Recorded Investment [Line Items]
Total loans	20,553
Commercial, Industrial and Other (including PPP) | 7 - Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,280
Commercial, Industrial and Other (including PPP) | 8 - Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0
Commercial, Industrial and Other (including PPP) | 9 - Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans	0
Commercial, industrial and other
Financing Receivable, Recorded Investment [Line Items]
Total loans	402,239	431,934
Commercial, industrial and other | 1
Financing Receivable, Recorded Investment [Line Items]
Total loans		898
Commercial, industrial and other | 2
Financing Receivable, Recorded Investment [Line Items]
Total loans		17,988
Commercial, industrial and other | 3
Financing Receivable, Recorded Investment [Line Items]
Total loans		39,112
Commercial, industrial and other | 4
Financing Receivable, Recorded Investment [Line Items]
Total loans		107,376
Commercial, industrial and other | 5
Financing Receivable, Recorded Investment [Line Items]
Total loans		215,975
Commercial, industrial and other | 5W - Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans		30,192
Commercial, industrial and other | 6 - Other assets especially mentioned
Financing Receivable, Recorded Investment [Line Items]
Total loans		11,328
Commercial, industrial and other | 7 - Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans		9,065
Commercial, industrial and other | 8 - Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans		0
Commercial, industrial and other | 9 - Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans		0
Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	299,441	335,169
Real estate - construction | 1
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Real estate - construction | 2
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Real estate - construction | 3
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Real estate - construction | 4
Financing Receivable, Recorded Investment [Line Items]
Total loans	18,674	17,941
Real estate - construction | 5
Financing Receivable, Recorded Investment [Line Items]
Total loans	239,847	307,824
Real estate - construction | 5W - Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans	27,106	6,959
Real estate - construction | 6 - Other assets especially mentioned
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,119	0
Real estate - construction | 7 - Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,695	2,445
Real estate - construction | 8 - Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Real estate - construction | 9 - Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Total Commercial Loans
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,989,155	4,356,696
Total Commercial Loans | 1
Financing Receivable, Recorded Investment [Line Items]
Total loans	326,662	898
Total Commercial Loans | 2
Financing Receivable, Recorded Investment [Line Items]
Total loans	16,730	17,988
Total Commercial Loans | 3
Financing Receivable, Recorded Investment [Line Items]
Total loans	107,835	113,184
Total Commercial Loans | 4
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,013,000	1,091,142
Total Commercial Loans | 5
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,377,012	2,856,662
Total Commercial Loans | 5W - Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans	922,756	137,498
Total Commercial Loans | 6 - Other assets especially mentioned
Financing Receivable, Recorded Investment [Line Items]
Total loans	129,580	66,766
Total Commercial Loans | 7 - Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	95,580	72,558
Total Commercial Loans | 8 - Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Total Commercial Loans | 9 - Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 0	$ 0