Fair Value Measurements - Carrying Values and Fair Values of Financial Instruments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
ASSETS
Securities available-for-sale	$ 655,829		$ 640,273
FHLB and other restricted stock	19,729		15,135
LIABILITIES
Junior subordinated debt securities	50,619		45,619
Carrying Value [Member]
ASSETS
Cash and due from banks, including interest-bearing deposits	124,737	[1]	109,580	[1]
Securities available-for-sale	655,829	[1]	640,273	[1]
Loans held for sale	6,126	[1]	2,970	[1]
Portfolio loans, net of unearned income	4,683,698	[1]	3,868,746	[1]
Bank owned life insurance	78,738	[1]	62,252	[1]
FHLB and other restricted stock	19,729	[1]	15,135	[1]
Trading securities held in a Rabbi Trust	3,505	[1]	3,456	[1]
Mortgage servicing rights	2,788	[1]	2,817	[1]
LIABILITIES
Deposits	4,828,531	[1]	3,908,842	[1]
Securities sold under repurchase agreements	46,721	[1]	30,605	[1]
Short-term borrowings	199,573	[1]	290,000	[1]
Long-term borrowings	18,838	[1]	19,442	[1]
Junior subordinated debt securities	50,619	[1]	45,619	[1]
Carrying Value [Member] | Interest Rate Swaps [Member]
ASSETS
Derivative financial assets	14,020	[1]	12,981	[1]
LIABILITIES
Derivative financial liabilities	13,979	[1]	12,953	[1]
Carrying Value [Member] | Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets	371	[1]	235	[1]
Carrying Value [Member] | Forward Sale Contracts [Member]
LIABILITIES
Derivative financial liabilities	74	[1]	57	[1]
Fair Value Measurements [Member]
ASSETS
Cash and due from banks, including interest-bearing deposits	124,737		109,580
Securities available-for-sale	655,829		640,273
Loans held for sale	6,160		2,991
Portfolio loans, net of unearned income	4,673,187		3,827,634
Bank owned life insurance	78,738		62,252
FHLB and other restricted stock	19,729		15,135
Trading securities held in a Rabbi Trust	3,505		3,456
Mortgage servicing rights	2,865		2,934
LIABILITIES
Deposits	4,834,805		3,910,342
Securities sold under repurchase agreements	46,721		30,605
Short-term borrowings	199,573		290,000
Long-term borrowings	19,928		20,462
Junior subordinated debt securities	50,619		45,619
Fair Value Measurements [Member] | Level 1 [Member]
ASSETS
Cash and due from banks, including interest-bearing deposits	124,737		109,580
Securities available-for-sale			178
Trading securities held in a Rabbi Trust	3,505		3,456
Fair Value Measurements [Member] | Level 2 [Member]
ASSETS
Securities available-for-sale	655,829		640,095
Bank owned life insurance	78,738		62,252
Fair Value Measurements [Member] | Level 3 [Member]
ASSETS
Loans held for sale	6,160		2,991
Portfolio loans, net of unearned income	4,673,187		3,827,634
FHLB and other restricted stock	19,729		15,135
Mortgage servicing rights	2,865		2,934
LIABILITIES
Deposits	4,834,805		3,910,342
Securities sold under repurchase agreements	46,721		30,605
Short-term borrowings	199,573		290,000
Long-term borrowings	19,928		20,462
Junior subordinated debt securities	50,619		45,619
Fair Value Measurements [Member] | Interest Rate Swaps [Member]
ASSETS
Derivative financial assets	14,020		12,981
LIABILITIES
Derivative financial liabilities	13,979		12,953
Fair Value Measurements [Member] | Interest Rate Swaps [Member] | Level 2 [Member]
ASSETS
Derivative financial assets	14,020		12,981
LIABILITIES
Derivative financial liabilities	13,979		12,953
Fair Value Measurements [Member] | Interest Rate Lock Commitments [Member]
ASSETS
Derivative financial assets	371		235
Fair Value Measurements [Member] | Interest Rate Lock Commitments [Member] | Level 2 [Member]
ASSETS
Derivative financial assets	371		235
Fair Value Measurements [Member] | Forward Sale Contracts [Member]
LIABILITIES
Derivative financial liabilities	74		57
Fair Value Measurements [Member] | Forward Sale Contracts [Member] | Level 2 [Member]
LIABILITIES
Derivative financial liabilities	$ 74		$ 57

[1] As reported in the Consolidated Balance Sheets.