Loans Loans Acquired with Evidence of Deterioration (Detail) (USD $)	Sep. 30, 2013	May 01, 2013 First Lansing Bancorp, Inc. [Member]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities Acquired During Period [Line Items]
Certain Loans Acquired In Transfer Not Accounted fo as Debt Securities, Accretable Yield, To Be Amortized To Indem Asset	$ 40,500,000
Contractually required payments including interest		32,022,000
Less: Nonaccretable difference		8,890,000
Cash flows expected to be collected		23,132,000	[1]
Less: Accretable yield		2,055,000
Fair value of loans acquired with evidence of credit quality deterioration since origination		$ 21,077,000

[1] Represents undiscounted expected principal and interest cash flows at acquisition.