Fair Value Measurements - Carrying Values and Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
ASSETS
Securities available-for-sale	$ 640,273us-gaap_AvailableForSaleSecurities	$ 509,425us-gaap_AvailableForSaleSecurities
Federal Home Loan Bank and other restricted stock, at cost	15,135us-gaap_RestrictedInvestments	13,629us-gaap_RestrictedInvestments
LIABILITIES
Junior subordinated debt securities	45,619us-gaap_JuniorSubordinatedLongTermNotes	45,619us-gaap_JuniorSubordinatedLongTermNotes	90,619us-gaap_JuniorSubordinatedLongTermNotes
Carrying Value [Member]
ASSETS
Cash and due from banks, including interest-bearing deposits	109,580	108,356
Securities available-for-sale	640,273	509,425
Loans held for sale	2,970	2,136
Portfolio loans, net of unearned income	3,868,746	3,566,199
Bank owned life insurance	62,252	60,480
Federal Home Loan Bank and other restricted stock, at cost	15,135	13,629
Trading securities held in a Rabbi Trust	3,456	2,864
Mortgage servicing rights	2,817	2,919
LIABILITIES
Deposits	3,908,842	3,672,308
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	30,605	33,847
Short-term Debt, Fair Value	290,000	140,000
Long-term Debt, Fair Value	19,442	21,810
Junior subordinated debt securities	45,619	45,619
Carrying Value [Member] \| Interest Rate Swaps [Member]
ASSETS
Derivative financial assets	12,981	13,698
LIABILITIES
Derivative financial liabilities	12,953	13,647
Carrying Value [Member] \| Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets	235	85
Carrying Value [Member] \| Forward Sale Contracts [Member]
ASSETS
Derivative financial assets		34
LIABILITIES
Derivative financial liabilities	57
Fair Value Measurements [Member]
ASSETS
Cash and due from banks, including interest-bearing deposits	109,580	108,356
Securities available-for-sale	640,273	509,425
Loans held for sale	2,991	2,139
Portfolio loans, net of unearned income	3,827,634	3,538,072
Bank owned life insurance	62,252	60,480
Federal Home Loan Bank and other restricted stock, at cost	15,135	13,629
Trading securities held in a Rabbi Trust	3,456	2,864
Mortgage servicing rights	2,934	3,143
LIABILITIES
Deposits	3,910,342	3,673,624
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	30,605	33,847
Short-term Debt, Fair Value	290,000	140,000
Long-term Debt, Fair Value	20,462	22,924
Junior subordinated debt securities	45,619	45,619
Fair Value Measurements [Member] \| Level 1 [Member]
ASSETS
Cash and due from banks, including interest-bearing deposits	109,580	108,356
Securities available-for-sale	178	202
Trading securities held in a Rabbi Trust	3,456	2,864
Fair Value Measurements [Member] \| Level 2 [Member]
ASSETS
Securities available-for-sale	640,095	509,223
Bank owned life insurance	62,252	60,480
Fair Value Measurements [Member] \| Level 3 [Member]
ASSETS
Securities available-for-sale		0
Loans held for sale	2,991	2,139
Portfolio loans, net of unearned income	3,827,634	3,538,072
Federal Home Loan Bank and other restricted stock, at cost	15,135	13,629
Mortgage servicing rights	2,934	3,143
LIABILITIES
Deposits	3,910,342	3,673,624
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	30,605	33,847
Short-term Debt, Fair Value	290,000	140,000
Long-term Debt, Fair Value	20,462	22,924
Junior subordinated debt securities	45,619	45,619
Fair Value Measurements [Member] \| Interest Rate Swaps [Member]
ASSETS
Derivative financial assets	12,981	13,698
LIABILITIES
Derivative financial liabilities	12,953	13,647
Fair Value Measurements [Member] \| Interest Rate Swaps [Member] \| Level 2 [Member]
ASSETS
Derivative financial assets	12,981	13,698
LIABILITIES
Derivative financial liabilities	12,953	13,647
Fair Value Measurements [Member] \| Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets	235	85
Fair Value Measurements [Member] \| Interest Rate Lock Commitments [Member] \| Level 2 [Member]
ASSETS
Derivative financial assets	235	85
Fair Value Measurements [Member] \| Forward Sale Contracts [Member]
ASSETS
Derivative financial assets		34
LIABILITIES
Derivative financial liabilities	57
Fair Value Measurements [Member] \| Forward Sale Contracts [Member] \| Level 2 [Member]
ASSETS
Derivative financial assets		34
LIABILITIES
Derivative financial liabilities	$ 57

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562