Fair Value Measurement - Estimated Fair Values of Financial Instruments that are Reported at Amortized Cost in Consolidated Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Financial assets:
Cash and due from banks	$ 76,915		$ 81,086
Securities held to maturity	240,504	0	0
Indemnification asset	206		1,997
Financial liabilities:
Other borrowings	6,335		9,197
Junior subordinated debt	41,238		41,238
Level 3 [Member]
Financial assets:
Securities held to maturity	0		0
Contract Amount [Member] | Level 3 [Member]
Off-balance sheet:
Commitments	555,386		557,254
Standby letters of credit	2,601		2,905
Overdraft privilege commitments	68,932		69,675
Fair Value [Member] | Level 3 [Member]
Financial assets:
Loans, net	1,760,274		1,607,044
Indemnification asset	206		1,997
Off-balance sheet:
Commitments	5,554		5,573
Standby letters of credit	26		29
Overdraft privilege commitments	689		697
Fair Value [Member] | Level 1 [Member]
Financial assets:
Cash and due from banks	76,915		81,086
Cash at Federal Reserve and other banks	521,453		667,813
Fair Value [Member] | Level 2 [Member]
Financial assets:
Securities held to maturity	233,807
Restricted equity securities	9,163		9,647
Loans held for sale	2,270		12,053
Financial liabilities:
Deposits	2,411,402		2,291,841
Other borrowings	6,335		9,197
Junior subordinated debt	25,774		28,042
Carrying Amount [Member] | Level 3 [Member]
Financial assets:
Loans, net	1,672,007		1,522,175
Indemnification asset	206		1,997
Carrying Amount [Member] | Level 1 [Member]
Financial assets:
Cash and due from banks	76,915		81,086
Cash at Federal Reserve and other banks	521,453		667,813
Carrying Amount [Member] | Level 2 [Member]
Financial assets:
Securities held to maturity	240,504
Restricted equity securities	9,163		9,647
Loans held for sale	2,270		12,053
Financial liabilities:
Deposits	2,410,483		2,289,702
Other borrowings	6,335		9,197
Junior subordinated debt	$ 41,238		$ 41,238