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	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	$ 3,668	$ 3,185
Additions		1,758
Accretion	(385)	(288)
Reclassification from nonaccretable difference	0	0
Disposals	(166)	(95)
Balance at June 30	3,117	4,560
Heartland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	2,400	3,185
Accretion	(205)	(288)
Reclassification from nonaccretable difference	0	0
Disposals	(117)	(95)
Balance at June 30	2,078	2,802
Summit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at January 1	1,268
Additions		1,758
Accretion	(180)
Reclassification from nonaccretable difference	0	0
Disposals	(49)
Balance at June 30	$ 1,039	$ 1,758

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

6 Months Ended

Jun. 30, 2015

Jun. 30, 2014

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

Balance at January 1

$ 3,668

$ 3,185

Additions

1,758

Accretion

(385)

(288)