Accounting for Certain Loans Acquired in a Transfer - Accretable Yield or Income Expected to be Collected (Detail) (Loans Purchased With Evidence Of Credit Deterioration [Member], USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2014	Sep. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	$ 3,185	$ 6,111
Additions	1,688
Accretion	(647)	(1,016)
Reclassification from nonaccreatable difference
Disposals	(256)	(1,629)
Balance at September 30	3,970	3,466
Heartland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	3,185	6,111
Accretion	(425)	(1,016)
Reclassification from nonaccreatable difference
Disposals	(210)	(1,629)
Balance at September 30	2,550	3,466
Summit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Additions	1,688
Accretion	(222)
Reclassification from nonaccreatable difference
Disposals	(46)
Balance at September 30	$ 1,420

Accounting for Certain Loans Acquired in a Transfer - Accretable Yield or Income Expected to be Collected (Detail) (Loans Purchased With Evidence Of Credit Deterioration [Member], USD $)
In Thousands, unless otherwise specified

9 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Accounts, Notes, Loans and Financing Receivable [Line Items]

Balance at January 1

$ 3,185

$ 6,111

Additions

1,688

Accretion

(647)

(1,016)