Loans - (Loan Delinquency) (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Loans [Line Items]
Total loans	$ 2,587,673	$ 2,162,409
Commercial Loan [Member]
Loans [Line Items]
Total loans	1,052,776	795,396
Agriculture [Member]
Loans [Line Items]
Total loans	162,310	137,531
Commercial Real Estate [Member]
Loans [Line Items]
Total loans	655,219	561,594
Residential Real Estate Segment [Member]
Loans [Line Items]
Total loans	684,002	632,700
Consumer [Member]
Loans [Line Items]
Total loans	33,366	35,188
Non ASC 310-30 [Member]
Loans [Line Items]
Total loans	2,384,843	1,882,764
Non ASC 310-30 [Member] | Commercial Loan [Member]
Loans [Line Items]
Total loans	1,039,769	772,440
Non ASC 310-30 [Member] | Agriculture [Member]
Loans [Line Items]
Total loans	145,558	118,468
Non ASC 310-30 [Member] | Commercial Real Estate [Member]
Loans [Line Items]
Total loans	506,331	369,264
Non ASC 310-30 [Member] | Residential Real Estate Segment [Member]
Loans [Line Items]
Total loans	662,550	591,939
Non ASC 310-30 [Member] | Consumer [Member]
Loans [Line Items]
Total loans	30,635	30,653
ASC 310-30 [Member]
Loans [Line Items]
Total loans	202,830	279,645
ASC 310-30 [Member] | Commercial Loan [Member]
Loans [Line Items]
Total loans	13,007	22,956
ASC 310-30 [Member] | Agriculture [Member]
Loans [Line Items]
Total loans	16,752	19,063
ASC 310-30 [Member] | Commercial Real Estate [Member]
Loans [Line Items]
Total loans	148,888	192,330
ASC 310-30 [Member] | Residential Real Estate Segment [Member]
Loans [Line Items]
Total loans	21,452	40,761
ASC 310-30 [Member] | Consumer [Member]
Loans [Line Items]
Total loans	2,731	4,535
Total Loans [Member]
Loans [Line Items]
Total past due	39,745	45,417
Current	2,547,928	2,116,992
Total loans	2,587,673	2,162,409
Loans 90 days past due and still accruing	15,927	34,097
Non- accrual	25,647	10,813
Total Loans [Member] | Non ASC 310-30 [Member]
Loans [Line Items]
Total past due	20,042	4,565
Current	2,364,801	1,878,199
Total loans	2,384,843	1,882,764
Loans 90 days past due and still accruing	166	263
Non- accrual	25,647	10,813
Total Loans [Member] | Non ASC 310-30 [Member] | Commercial Construction [Member]
Loans [Line Items]
Total past due	547
Current	29,596	11,748
Total loans	30,143	11,748
Non- accrual	188
Total Loans [Member] | Non ASC 310-30 [Member] | Commercial Acquisition/Development [Member]
Loans [Line Items]
Total past due		41
Current	5,575	4,532
Total loans	5,575	4,573
Total Loans [Member] | Non ASC 310-30 [Member] | Multifamily [Member]
Loans [Line Items]
Total past due	60
Current	9,813	10,856
Total loans	9,873	10,856
Loans 90 days past due and still accruing		(1)
Non- accrual	22
Total Loans [Member] | Non ASC 310-30 [Member] | Owner-Occupied [Member]
Loans [Line Items]
Total past due	547	515
Current	184,072	119,710
Total loans	184,619	120,225
Non- accrual	1,273	843
Total Loans [Member] | Non ASC 310-30 [Member] | Non Owner-Occupied [Member]
Loans [Line Items]
Total past due	3,490	380
Current	272,631	221,482
Total loans	276,121	221,862
Non- accrual	1,013	222
Total Loans [Member] | Non ASC 310-30 [Member] | Total Commercial Real Estate [Member]
Loans [Line Items]
Total past due	4,644	936
Current	501,687	368,328
Total loans	506,331	369,264
Loans 90 days past due and still accruing		(1)
Non- accrual	2,496	1,065
Total Loans [Member] | Non ASC 310-30 [Member] | Senior lien
Loans [Line Items]
Total past due	4,301	2,513
Current	610,192	537,022
Total loans	614,493	539,535
Loans 90 days past due and still accruing	124
Non- accrual	3,713	4,335
Total Loans [Member] | Non ASC 310-30 [Member] | Junior lien
Loans [Line Items]
Total past due	730	235
Current	47,327	52,169
Total loans	48,057	52,404
Loans 90 days past due and still accruing	6
Non- accrual	584	476
Total Loans [Member] | Non ASC 310-30 [Member] | Commercial Loan [Member]
Loans [Line Items]
Total past due	8,343	498
Current	1,031,426	771,942
Total loans	1,039,769	772,440
Loans 90 days past due and still accruing		215
Non- accrual	16,838	4,215
Total Loans [Member] | Non ASC 310-30 [Member] | Agriculture [Member]
Loans [Line Items]
Total past due	1,721	57
Current	143,837	118,411
Total loans	145,558	118,468
Loans 90 days past due and still accruing		10
Non- accrual	1,984	495
Total Loans [Member] | Non ASC 310-30 [Member] | Residential Real Estate Segment [Member]
Loans [Line Items]
Total past due	5,031	2,748
Current	657,519	589,191
Total loans	662,550	591,939
Loans 90 days past due and still accruing	130
Non- accrual	4,297	4,811
Total Loans [Member] | Non ASC 310-30 [Member] | Consumer [Member]
Loans [Line Items]
Total past due	303	326
Current	30,332	30,327
Total loans	30,635	30,653
Loans 90 days past due and still accruing	36	39
Non- accrual	32	227
Total Loans [Member] | ASC 310-30 [Member]
Loans [Line Items]
Total past due	19,703	40,852
Current	183,127	238,793
Total loans	202,830	279,645
Loans 90 days past due and still accruing	15,761	33,834
Total Loans [Member] | ASC 310-30 [Member] | Commercial Loan [Member]
Loans [Line Items]
Total past due	1,404	1,907
Current	11,603	21,049
Total loans	13,007	22,956
Loans 90 days past due and still accruing	217	1,754
Total Loans [Member] | ASC 310-30 [Member] | Agriculture [Member]
Loans [Line Items]
Total past due	511	367
Current	16,241	18,696
Total loans	16,752	19,063
Loans 90 days past due and still accruing	511	367
Total Loans [Member] | ASC 310-30 [Member] | Commercial Real Estate [Member]
Loans [Line Items]
Total past due	17,103	31,669
Current	131,785	160,661
Total loans	148,888	192,330
Loans 90 days past due and still accruing	14,931	31,013
Total Loans [Member] | ASC 310-30 [Member] | Residential Real Estate Segment [Member]
Loans [Line Items]
Total past due	612	6,486
Current	20,840	34,275
Total loans	21,452	40,761
Loans 90 days past due and still accruing	97	646
Total Loans [Member] | ASC 310-30 [Member] | Consumer [Member]
Loans [Line Items]
Total past due	73	423
Current	2,658	4,112
Total loans	2,731	4,535
Loans 90 days past due and still accruing	5	54
Total Loans [Member] | 30-59 Days Past Due
Loans [Line Items]
Total past due	11,084	4,541
Total Loans [Member] | 30-59 Days Past Due | Non ASC 310-30 [Member]
Loans [Line Items]
Total past due	8,232	1,442
Total Loans [Member] | 30-59 Days Past Due | Non ASC 310-30 [Member] | Commercial Construction [Member]
Loans [Line Items]
Total past due	359
Total Loans [Member] | 30-59 Days Past Due | Non ASC 310-30 [Member] | Commercial Acquisition/Development [Member]
Loans [Line Items]
Total past due		41
Total Loans [Member] | 30-59 Days Past Due | Non ASC 310-30 [Member] | Owner-Occupied [Member]
Loans [Line Items]
Total past due	370	336
Total Loans [Member] | 30-59 Days Past Due | Non ASC 310-30 [Member] | Non Owner-Occupied [Member]
Loans [Line Items]
Total past due	2,340	158
Total Loans [Member] | 30-59 Days Past Due | Non ASC 310-30 [Member] | Total Commercial Real Estate [Member]
Loans [Line Items]
Total past due	3,069	535
Total Loans [Member] | 30-59 Days Past Due | Non ASC 310-30 [Member] | Senior lien
Loans [Line Items]
Total past due	1,909	378
Total Loans [Member] | 30-59 Days Past Due | Non ASC 310-30 [Member] | Junior lien
Loans [Line Items]
Total past due	299	133
Total Loans [Member] | 30-59 Days Past Due | Non ASC 310-30 [Member] | Commercial Loan [Member]
Loans [Line Items]
Total past due	2,275	83
Total Loans [Member] | 30-59 Days Past Due | Non ASC 310-30 [Member] | Agriculture [Member]
Loans [Line Items]
Total past due	441	47
Total Loans [Member] | 30-59 Days Past Due | Non ASC 310-30 [Member] | Residential Real Estate Segment [Member]
Loans [Line Items]
Total past due	2,208	511
Total Loans [Member] | 30-59 Days Past Due | Non ASC 310-30 [Member] | Consumer [Member]
Loans [Line Items]
Total past due	239	266
Total Loans [Member] | 30-59 Days Past Due | ASC 310-30 [Member]
Loans [Line Items]
Total past due	2,852	3,099
Total Loans [Member] | 30-59 Days Past Due | ASC 310-30 [Member] | Commercial Loan [Member]
Loans [Line Items]
Total past due	1,187	152
Total Loans [Member] | 30-59 Days Past Due | ASC 310-30 [Member] | Commercial Real Estate [Member]
Loans [Line Items]
Total past due	1,235	564
Total Loans [Member] | 30-59 Days Past Due | ASC 310-30 [Member] | Residential Real Estate Segment [Member]
Loans [Line Items]
Total past due	411	2,014
Total Loans [Member] | 30-59 Days Past Due | ASC 310-30 [Member] | Consumer [Member]
Loans [Line Items]
Total past due	19	369
Total Loans [Member] | 60-89 Days Past Due
Loans [Line Items]
Total past due	8,859	5,518
Total Loans [Member] | 60-89 Days Past Due | Non ASC 310-30 [Member]
Loans [Line Items]
Total past due	7,770	1,600
Total Loans [Member] | 60-89 Days Past Due | Non ASC 310-30 [Member] | Commercial Construction [Member]
Loans [Line Items]
Total past due	188
Total Loans [Member] | 60-89 Days Past Due | Non ASC 310-30 [Member] | Multifamily [Member]
Loans [Line Items]
Total past due	38
Total Loans [Member] | 60-89 Days Past Due | Non ASC 310-30 [Member] | Owner-Occupied [Member]
Loans [Line Items]
Total past due	111	78
Total Loans [Member] | 60-89 Days Past Due | Non ASC 310-30 [Member] | Non Owner-Occupied [Member]
Loans [Line Items]
Total past due	182
Total Loans [Member] | 60-89 Days Past Due | Non ASC 310-30 [Member] | Total Commercial Real Estate [Member]
Loans [Line Items]
Total past due	519	78
Total Loans [Member] | 60-89 Days Past Due | Non ASC 310-30 [Member] | Senior lien
Loans [Line Items]
Total past due	911	1,403
Total Loans [Member] | 60-89 Days Past Due | Non ASC 310-30 [Member] | Junior lien
Loans [Line Items]
Total past due	237	1
Total Loans [Member] | 60-89 Days Past Due | Non ASC 310-30 [Member] | Commercial Loan [Member]
Loans [Line Items]
Total past due	6,019	97
Total Loans [Member] | 60-89 Days Past Due | Non ASC 310-30 [Member] | Agriculture [Member]
Loans [Line Items]
Total past due	58
Total Loans [Member] | 60-89 Days Past Due | Non ASC 310-30 [Member] | Residential Real Estate Segment [Member]
Loans [Line Items]
Total past due	1,148	1,404
Total Loans [Member] | 60-89 Days Past Due | Non ASC 310-30 [Member] | Consumer [Member]
Loans [Line Items]
Total past due	26	21
Total Loans [Member] | 60-89 Days Past Due | ASC 310-30 [Member]
Loans [Line Items]
Total past due	1,089	3,918
Total Loans [Member] | 60-89 Days Past Due | ASC 310-30 [Member] | Commercial Real Estate [Member]
Loans [Line Items]
Total past due	936	92
Total Loans [Member] | 60-89 Days Past Due | ASC 310-30 [Member] | Residential Real Estate Segment [Member]
Loans [Line Items]
Total past due	104	3,826
Total Loans [Member] | 60-89 Days Past Due | ASC 310-30 [Member] | Consumer [Member]
Loans [Line Items]
Total past due	49
Total Loans [Member] | Greater than 90 Days Past Due
Loans [Line Items]
Total past due	19,802	35,358
Total Loans [Member] | Greater than 90 Days Past Due | Non ASC 310-30 [Member]
Loans [Line Items]
Total past due	4,040	1,523
Total Loans [Member] | Greater than 90 Days Past Due | Non ASC 310-30 [Member] | Multifamily [Member]
Loans [Line Items]
Total past due	22
Total Loans [Member] | Greater than 90 Days Past Due | Non ASC 310-30 [Member] | Owner-Occupied [Member]
Loans [Line Items]
Total past due	66	101
Total Loans [Member] | Greater than 90 Days Past Due | Non ASC 310-30 [Member] | Non Owner-Occupied [Member]
Loans [Line Items]
Total past due	968	222
Total Loans [Member] | Greater than 90 Days Past Due | Non ASC 310-30 [Member] | Total Commercial Real Estate [Member]
Loans [Line Items]
Total past due	1,056	323
Total Loans [Member] | Greater than 90 Days Past Due | Non ASC 310-30 [Member] | Senior lien
Loans [Line Items]
Total past due	1,481	732
Total Loans [Member] | Greater than 90 Days Past Due | Non ASC 310-30 [Member] | Junior lien
Loans [Line Items]
Total past due	194	101
Total Loans [Member] | Greater than 90 Days Past Due | Non ASC 310-30 [Member] | Commercial Loan [Member]
Loans [Line Items]
Total past due	49	318
Total Loans [Member] | Greater than 90 Days Past Due | Non ASC 310-30 [Member] | Agriculture [Member]
Loans [Line Items]
Total past due	1,222	10
Total Loans [Member] | Greater than 90 Days Past Due | Non ASC 310-30 [Member] | Residential Real Estate Segment [Member]
Loans [Line Items]
Total past due	1,675	833
Total Loans [Member] | Greater than 90 Days Past Due | Non ASC 310-30 [Member] | Consumer [Member]
Loans [Line Items]
Total past due	38	39
Total Loans [Member] | Greater than 90 Days Past Due | ASC 310-30 [Member]
Loans [Line Items]
Total past due	15,762	33,835
Total Loans [Member] | Greater than 90 Days Past Due | ASC 310-30 [Member] | Commercial Loan [Member]
Loans [Line Items]
Total past due	217	1,755
Total Loans [Member] | Greater than 90 Days Past Due | ASC 310-30 [Member] | Agriculture [Member]
Loans [Line Items]
Total past due	511	367
Total Loans [Member] | Greater than 90 Days Past Due | ASC 310-30 [Member] | Commercial Real Estate [Member]
Loans [Line Items]
Total past due	14,932	31,013
Total Loans [Member] | Greater than 90 Days Past Due | ASC 310-30 [Member] | Residential Real Estate Segment [Member]
Loans [Line Items]
Total past due	97	646
Total Loans [Member] | Greater than 90 Days Past Due | ASC 310-30 [Member] | Consumer [Member]
Loans [Line Items]
Total past due	5	54
Non Accrual [Member]
Loans [Line Items]
Non- accrual	$ 25,600	$ 10,800