Loans and Allowance for Loan Losses - Internal Loan Grading by Class of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 4,578,393	$ 4,400,232
Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	591,089	571,631
Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,128,109	1,123,396
Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	330,731	325,413
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	758,117	748,229
Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,208,326	1,051,185
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	284,157	283,877
Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	144,548	141,482
Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	133,316	155,019
Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,739,534	3,642,438
Grade 1 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	474,155	464,504
Grade 1 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	941,448	933,743
Grade 1 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	289,912	284,893
Grade 1 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	607,861	614,338
Grade 1 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	947,575	856,318
Grade 1 [Member] | Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	263,875	263,442
Grade 1 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	137,753	132,254
Grade 1 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	76,955	92,946
Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	731,646	647,509
Grade 2 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	101,757	89,978
Grade 2 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	169,968	169,561
Grade 2 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	33,676	32,889
Grade 2 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	134,189	119,018
Grade 2 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	234,258	170,865
Grade 2 [Member] | Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	17,473	17,154
Grade 2 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	5,450	5,376
Grade 2 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	34,875	42,668
Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	90,268	82,136
Grade 3 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	14,536	16,220
Grade 3 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	14,759	14,404
Grade 3 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	5,805	5,987
Grade 3 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	10,918	9,382
Grade 3 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	22,652	19,101
Grade 3 [Member] | Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,093	2,640
Grade 3 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,115	1,514
Grade 3 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	18,390	12,888
Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	16,945	28,149
Grade 4 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	641	929
Grade 4 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,934	5,688
Grade 4 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,338	1,644
Grade 4 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	5,149	5,491
Grade 4 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,841	4,901
Grade 4 [Member] | Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	716	641
Grade 4 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	230	2,338
Grade 4 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 3,096	$ 6,517