Loans and Allowance for Credit Losses - Schedule of Accretable Yield of Noncovered Loans, or Income Expected to be Collected (Detail) (Non Covered Loans [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at January 1	$ 26,791
New loans purchased	1,812
Accretion of income	(2,880)
Reclassifications from (to) nonaccretable difference	1,657
Disposals/other adjustments	72
Balance at March 31	27,452
Monroe [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at January 1	3,564
Accretion of income	(362)
Reclassifications from (to) nonaccretable difference	9
Balance at March 31	3,211
Integra Noncovered [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at January 1	1,389
Accretion of income	(147)
Reclassifications from (to) nonaccretable difference	71
Balance at March 31	1,313
IBT [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at January 1	13,354
Accretion of income	(1,403)
Reclassifications from (to) nonaccretable difference	519
Balance at March 31	12,470
Tower [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at January 1	4,559
Accretion of income	(322)
Reclassifications from (to) nonaccretable difference	(163)
Disposals/other adjustments	32
Balance at March 31	4,106
United [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at January 1	1,516
Accretion of income	(225)
Reclassifications from (to) nonaccretable difference	466
Disposals/other adjustments	40
Balance at March 31	1,797
LSB [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at January 1	2,409
Accretion of income	(293)
Reclassifications from (to) nonaccretable difference	755
Balance at March 31	2,871
Founders Financial Corporation [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
New loans purchased	1,812
Accretion of income	(128)
Balance at March 31	$ 1,684