Regulatory Matters - Actual and Required Capital Ratios of Bank (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Dec. 31, 2014
Parent [Member]
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Actual, Amount	$ 486,632	$ 474,436
Tier 1 Capital (to Risk Weighted Assets), Actual, Amount	448,240	435,950
Tier 1 Capital (to Average Assets), Actual, Amount	$ 448,240	$ 435,950
Total Capital (to Risk Weighted Assets), Actual, Ratio	14.73%	15.09%
Tier 1 Capital (to Risk Weighted Assets), Actual, Ratio	13.57%	13.86%
Tier 1 Capital (to Average Assets), Actual, Ratio	10.40%	10.79%
Parent [Member] | Basel III Phase-in Schedule [Member]
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	$ 264,227	$ 251,555
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	198,170	188,666
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Amount	$ 172,473	$ 161,562
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	8.00%	8.00%	8.00%
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	6.00%	6.00%	4.00%
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Ratio	4.00%	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	$ 346,798	$ 330,165
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	280,741	267,277
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Amount	$ 172,473	$ 161,562
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	10.50%	10.50%
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	8.50%	8.50%
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Ratio	4.00%	4.00%
Parent [Member] | Common Stock [Member]
Schedule of Capitalization [Line Items]
Tier 1 Capital (to Risk Weighted Assets), Actual, Amount	$ 395,669	$ 385,747
Tier 1 Capital (to Risk Weighted Assets), Actual, Ratio	11.98%	12.27%
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	$ 148,628	$ 141,499
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	4.50%	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	$ 231,199	$ 220,110
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	7.00%	7.00%
Tri Countries Bank [Member]
Schedule of Capitalization [Line Items]
Total Capital (to Risk Weighted Assets), Actual, Amount	$ 484,512	$ 473,327
Tier 1 Capital (to Risk Weighted Assets), Actual, Amount	446,120	434,841
Tier 1 Capital (to Average Assets), Actual, Amount	$ 446,120	$ 434,841
Total Capital (to Risk Weighted Assets), Actual, Ratio	14.68%	15.06%
Tier 1 Capital (to Risk Weighted Assets), Actual, Ratio	13.51%	13.84%
Tier 1 Capital (to Average Assets), Actual, Ratio	10.35%	10.76%
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 330,111	$ 314,272
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	264,089	251,418
Tier 1 Capital (to Average Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 215,584	$ 202,002
Total Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	10.00%	10.00%	10.00%
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	8.00%	8.00%	6.00%
Tier 1 Capital (to Average Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	5.00%	5.00%	4.00%
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	$ 264,089	$ 251,418
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	198,067	188,563
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Amount	$ 172,467	$ 161,601
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	8.00%	8.00%	8.00%
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	6.00%	6.00%	4.00%
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Ratio	4.00%	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	$ 346,617	$ 329,985
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Amount	280,595	267,131
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Amount	$ 172,467	$ 161,601
Total Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	10.50%	10.50%
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	8.50%	8.50%
Tier 1 Capital (to Average Assets), Minimum Capital Requirement, Ratio	4.00%	4.00%
Tri Countries Bank [Member] | Common Stock [Member]
Schedule of Capitalization [Line Items]
Tier 1 Capital (to Risk Weighted Assets), Actual, Amount	$ 446,120	$ 434,841
Tier 1 Capital (to Risk Weighted Assets), Actual, Ratio	13.51%	13.84%
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Amount	$ 214,572	$ 204,277
Tier 1 Capital (to Risk Weighted Assets), Minimum To Be Well Capitalized Under Prompt Corrective Action Provisions, Ratio	6.50%	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	$ 148,550	$ 141,422
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	4.50%	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	$ 231,078	$ 219,990
Tier 1 Capital (to Risk Weighted Assets), Minimum Capital Requirement, Ratio	7.00%	7.00%