Fair Value Measurement - Carrying Values and Fair Values of Financial Instruments (Detail) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
ASSETS
Securities available-for-sale		$ 660,046	$ 640,273
FHLB and other restricted stock		20,352	15,135
LIABILITIES
Junior subordinated debt securities		45,619	45,619
Carrying Value [Member]
ASSETS
Cash and due from banks, including interest-bearing deposits	[1]	115,347	109,580
Securities available-for-sale	[1]	660,046	640,273
Loans held for sale	[1]	13,794	2,970
Portfolio loans, net of unearned income	[1]	4,925,963	3,868,746
Bank owned life insurance	[1]	79,894	62,252
FHLB and other restricted stock	[1]	20,352	15,135
Trading securities held in a Rabbi Trust	[1]	3,690	3,456
Mortgage servicing rights	[1]	3,083	2,817
LIABILITIES
Deposits	[1]	4,877,409	3,908,842
Securities sold under repurchase agreements	[1]	42,971	30,605
Short-term borrowings	[1]	280,000	290,000
Long-term borrowings	[1]	117,613	19,442
Junior subordinated debt securities	[1]	45,619	45,619
Carrying Value [Member] | Interest Rate Swaps [Member]
ASSETS
Derivative financial assets	[1]	14,232	12,981
LIABILITIES
Derivative financial liabilities	[1]	14,184	12,953
Carrying Value [Member] | Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets	[1]	574	235
Carrying Value [Member] | Forward Sale Contracts [Member]
LIABILITIES
Derivative financial liabilities	[1]	126	57
Fair Value Measurements [Member]
ASSETS
Cash and due from banks, including interest-bearing deposits		115,347	109,580
Securities available-for-sale		660,046	640,273
Loans held for sale		14,134	2,991
Portfolio loans, net of unearned income		4,902,661	3,827,634
Bank owned life insurance		79,894	62,252
FHLB and other restricted stock		20,352	15,135
Trading securities held in a Rabbi Trust		3,690	3,456
Mortgage servicing rights		3,170	2,934
LIABILITIES
Deposits		4,883,132	3,910,342
Securities sold under repurchase agreements		42,971	30,605
Short-term borrowings		280,000	290,000
Long-term borrowings		118,646	20,462
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		115,347	109,580
Securities available-for-sale		0	178
Loans held for sale		0	0
Portfolio loans, net of unearned income		0	0
Bank owned life insurance		0	0
FHLB and other restricted stock		0	0
Trading securities held in a Rabbi Trust		3,690	3,456
Mortgage servicing rights		0	0
LIABILITIES
Deposits		0	0
Securities sold under repurchase agreements		0	0
Short-term borrowings		0	0
Long-term borrowings		0	0
Junior subordinated debt securities		0	0
Fair Value Measurements [Member] | Level 2 [Member]
ASSETS
Cash and due from banks, including interest-bearing deposits		0	0
Securities available-for-sale		660,046	640,095
Loans held for sale		0	0
Portfolio loans, net of unearned income		0	0
Bank owned life insurance		79,894	62,252
FHLB and other restricted stock		0	0
Trading securities held in a Rabbi Trust		0	0
Mortgage servicing rights		0	0
LIABILITIES
Deposits		0	0
Securities sold under repurchase agreements		0	0
Short-term borrowings		0	0
Long-term borrowings		0	0
Junior subordinated debt securities		0	0
Fair Value Measurements [Member] | Level 3 [Member]
ASSETS
Cash and due from banks, including interest-bearing deposits		0	0
Securities available-for-sale		0	0
Loans held for sale		14,134	2,991
Portfolio loans, net of unearned income		4,902,661	3,827,634
Bank owned life insurance		0	0
FHLB and other restricted stock		20,352	15,135
Trading securities held in a Rabbi Trust		0	0
Mortgage servicing rights		3,170	2,934
LIABILITIES
Deposits		4,883,132	3,910,342
Securities sold under repurchase agreements		42,971	30,605
Short-term borrowings		280,000	290,000
Long-term borrowings		118,646	20,462
Junior subordinated debt securities		45,619	45,619
Fair Value Measurements [Member] | Interest Rate Swaps [Member]
ASSETS
Derivative financial assets		14,232	12,981
LIABILITIES
Derivative financial liabilities		14,184	12,953
Fair Value Measurements [Member] | Interest Rate Swaps [Member] | Level 1 [Member]
ASSETS
Derivative financial assets		0	0
LIABILITIES
Derivative financial liabilities		0	0
Fair Value Measurements [Member] | Interest Rate Swaps [Member] | Level 2 [Member]
ASSETS
Derivative financial assets		14,232	12,981
LIABILITIES
Derivative financial liabilities		14,184	12,953
Fair Value Measurements [Member] | Interest Rate Swaps [Member] | Level 3 [Member]
ASSETS
Derivative financial assets		0	0
LIABILITIES
Derivative financial liabilities		0	0
Fair Value Measurements [Member] | Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets		574	235
Fair Value Measurements [Member] | Interest Rate Lock Commitments [Member] | Level 1 [Member]
ASSETS
Derivative financial assets		0	0
Fair Value Measurements [Member] | Interest Rate Lock Commitments [Member] | Level 2 [Member]
ASSETS
Derivative financial assets		574	235
Fair Value Measurements [Member] | Interest Rate Lock Commitments [Member] | Level 3 [Member]
ASSETS
Derivative financial assets		0	0
Fair Value Measurements [Member] | Forward Sale Contracts [Member]
LIABILITIES
Derivative financial liabilities		126	57
Fair Value Measurements [Member] | Forward Sale Contracts [Member] | Level 1 [Member]
LIABILITIES
Derivative financial liabilities		0	0
Fair Value Measurements [Member] | Forward Sale Contracts [Member] | Level 2 [Member]
LIABILITIES
Derivative financial liabilities		126	57
Fair Value Measurements [Member] | Forward Sale Contracts [Member] | Level 3 [Member]
LIABILITIES
Derivative financial liabilities		$ 0	$ 0

[1] As reported in the Consolidated Balance Sheets.