Regulatory Matters - Actual and Required Capital Ratios of Bank (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount		$ 279,311
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount		167,587
Tier 1 Capital (to Average Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount		185,918
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio		10.00%
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio		6.00%
Tier 1 Capital (to Average Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio		5.00%
Parent [Member]
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Actual, Amount	444,192	436,955
Tier 1 Capital (to Risk Weighted Assets), Actual, Amount	407,722	401,971
Tier 1 Capital (to Average Assets), Actual, Amount	407,722	401,971
Total Capital (to Risk Weighted Assets), Actual, Ratio	15.23%	15.63%
Tier 1 Capital (to Risk Weighted Assets), Actual, Ratio	13.98%	14.38%
Tier 1 Capital (to Average Assets), Actual, Ratio	10.68%	10.80%
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount		223,603
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount		111,801
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Amount		148,819
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio		8.00%
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio		4.00%
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Ratio		4.00%
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	291,598
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	233,279
Tier 1 Capital (to Average Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	190,935
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	8.00%
Tier 1 Capital (to Average Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%
Parent [Member] | Basel III Phase-in Schedule [Member]
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	233,279
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	174,959
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Amount	152,748
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	8.00%
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	6.00%
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Ratio	4.00%
Parent [Member] | Basel III Fully Phased In [Member]
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	306,178
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	247,858
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Amount	152,748
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	10.50%
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	8.50%
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Ratio	4.00%
Parent [Member] | Common Stock [Member]
Schedule of Capitalization [Line Items]
Tier 1 Capital (to Risk Weighted Assets), Actual, Amount	353,131
Tier 1 Capital (to Risk Weighted Assets), Actual, Ratio	12.11%
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	189,426
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	6.50%
Parent [Member] | Common Stock [Member] | Basel III Phase-in Schedule [Member]
Schedule of Capitalization [Line Items]
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	131,219
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	4.50%
Parent [Member] | Common Stock [Member] | Basel III Fully Phased In [Member]
Schedule of Capitalization [Line Items]
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	204,119
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	7.00%
Tri Countries Bank [Member]
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Actual, Amount	442,590	433,286
Tier 1 Capital (to Risk Weighted Assets), Actual, Amount	406,142	398,325
Tier 1 Capital (to Average Assets), Actual, Amount	406,142	398,325
Total Capital (to Risk Weighted Assets), Actual, Ratio	15.19%	15.51%
Tier 1 Capital (to Risk Weighted Assets), Actual, Ratio	13.94%	14.26%
Tier 1 Capital (to Average Assets), Actual, Ratio	10.64%	10.71%
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount		223,449
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount		111,724
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Amount		148,734
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio		8.00%
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio		4.00%
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Ratio		4.00%
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	291,422
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	233,138
Tier 1 Capital (to Average Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	190,845
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	8.00%
Tier 1 Capital (to Average Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%
Tri Countries Bank [Member] | Basel III Phase-in Schedule [Member]
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	233,138
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	174,853
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Amount	152,676
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	8.00%
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	6.00%
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Ratio	4.00%
Tri Countries Bank [Member] | Basel III Fully Phased In [Member]
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	305,993
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	247,709
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Amount	152,676
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	10.50%
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	8.50%
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Ratio	4.00%
Tri Countries Bank [Member] | Common Stock [Member]
Schedule of Capitalization [Line Items]
Tier 1 Capital (to Risk Weighted Assets), Actual, Amount	406,142
Tier 1 Capital (to Risk Weighted Assets), Actual, Ratio	13.94%
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	189,539
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	6.50%
Tri Countries Bank [Member] | Common Stock [Member] | Basel III Phase-in Schedule [Member]
Schedule of Capitalization [Line Items]
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	131,140
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	4.50%
Tri Countries Bank [Member] | Common Stock [Member] | Basel III Fully Phased In [Member]
Schedule of Capitalization [Line Items]
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	$ 203,996
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	7.00%