Loans and Allowance for Loan Losses - Internal Loan Grading by Class of Loans (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 4,400,232	$ 4,232,048
Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	571,631	502,897
Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,123,396	1,110,760
Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	325,413	332,601
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	748,229	676,689
Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,051,185	984,762
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	283,877	268,869
Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	141,482	162,616
Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	155,019	192,854
Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	3,642,438	3,604,903
Grade 1 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	464,504	417,529
Grade 1 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	933,743	945,993
Grade 1 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	284,893	295,265
Grade 1 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	614,338	554,007
Grade 1 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	856,318	821,394
Grade 1 [Member] | Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	263,442	251,994
Grade 1 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	132,254	153,416
Grade 1 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	92,946	165,305
Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	647,509	547,814
Grade 2 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	89,978	76,749
Grade 2 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	169,561	156,159
Grade 2 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	32,889	29,793
Grade 2 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	119,018	111,879
Grade 2 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	170,865	140,384
Grade 2 [Member] | Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	17,154	14,433
Grade 2 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	5,376	5,851
Grade 2 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	42,668	12,566
Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	82,136	54,695
Grade 3 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	16,220	8,304
Grade 3 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	14,404	4,580
Grade 3 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	5,987	6,315
Grade 3 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	9,382	9,109
Grade 3 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	19,101	12,687
Grade 3 [Member] | Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,640	1,779
Grade 3 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,514	872
Grade 3 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	12,888	11,049
Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	28,149	24,559
Grade 4 [Member] | Real Estate [Member] | Non-residential Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	929	315
Grade 4 [Member] | Real Estate [Member] | Non-residential Real Estate Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	5,688	4,028
Grade 4 [Member] | Real Estate [Member] | Residential Real Estate Permanent Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,644	1,228
Grade 4 [Member] | Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	5,491	1,694
Grade 4 [Member] | Commercial and Financial [Member] | Non-consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	4,901	10,297
Grade 4 [Member] | Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	641	662
Grade 4 [Member] | Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,338	2,477
Grade 4 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 6,517	3,858
Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		77
Grade 5 [Member] | Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		1
Grade 5 [Member] | Acquired Loans [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans		$ 76