Loans and Other Real Estate - Company's Commercial Loan Portfolio (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 4,883,711	$ 4,419,045
Commercial, secured by real estate
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,431,709	3,057,779
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	72,155	69,995
Commercial, secured by real estate | 4
Financing Receivable, Recorded Investment [Line Items]
Total loans	937,855	933,577
Commercial, secured by real estate | 5
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,222,710	1,910,423
Commercial, secured by real estate | 5W - Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans	96,095	61,626
Commercial, secured by real estate | 6 - Other assets especially mentioned
Financing Receivable, Recorded Investment [Line Items]
Total loans	51,572	38,844
Commercial, secured by real estate | 7 - Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	51,322	43,314
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
Financing Receivable, Recorded Investment [Line Items]
Total loans	407,776	336,735
Commercial, industrial and other | 1
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,414	1,119
Commercial, industrial and other | 2
Financing Receivable, Recorded Investment [Line Items]
Total loans	19,465	18,462
Commercial, industrial and other | 3
Financing Receivable, Recorded Investment [Line Items]
Total loans	37,113	36,367
Commercial, industrial and other | 4
Financing Receivable, Recorded Investment [Line Items]
Total loans	96,762	91,145
Commercial, industrial and other | 5
Financing Receivable, Recorded Investment [Line Items]
Total loans	217,158	168,474
Commercial, industrial and other | 5W - Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans	17,997	7,798
Commercial, industrial and other | 6 - Other assets especially mentioned
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,942	2,033
Commercial, industrial and other | 7 - Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,925	11,337
Commercial, industrial and other | 8 - Doubtful
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial, industrial and other | 9 - Loss
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Real estate - construction
Financing Receivable, Recorded Investment [Line Items]
Total loans	305,738	319,545
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	17,086	17,375
Real estate - construction | 5
Financing Receivable, Recorded Investment [Line Items]
Total loans	274,322	297,625
Real estate - construction | 5W - Watch
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,738	3,493
Real estate - construction | 6 - Other assets especially mentioned
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,267	0
Real estate - construction | 7 - Substandard
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,325	1,052
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