Fair Value Disclosures - Assets, Liabilities and Off-balance Sheet Items Not Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Assets:
Held-to-maturity securities	$ 24,871	$ 41,061
Total assets	2,138
Deposits:
Time deposits	626,189	454,406
Subordinated notes	94,087	49,377
Fair Value [Member]
Assets:
Cash and short-term interest-earning assets	57,825	60,799
Held-to-maturity securities	24,871	41,061
Loans held for sale	5,943	4,708
Net loans and leases held for investment	3,193,886	2,099,082
Mortgage servicing rights	9,548	8,047
Other real estate owned		1,276
Total assets	3,292,073	2,214,973
Deposits:
Demand and savings deposits, non-maturity	2,631,378	1,939,954
Time deposits	628,096	455,527
Total deposits	3,259,474	2,395,481
Short-term borrowings	195,572	22,302
Long-term debt	130,157
Subordinated notes	95,188	50,375
Total liabilities	3,680,391	2,468,158
Off-Balance-Sheet:
Commitments to extend credit	(2,218)	(1,788)
Fair Value [Member] | Level 1 [Member]
Assets:
Cash and short-term interest-earning assets	57,825	60,799
Held-to-maturity securities	0	0
Loans held for sale	0	0
Net loans and leases held for investment	0	0
Mortgage servicing rights	0	0
Other real estate owned		0
Total assets	57,825	60,799
Deposits:
Demand and savings deposits, non-maturity	2,631,378	1,939,954
Time deposits	0	0
Total deposits	2,631,378	1,939,954
Short-term borrowings	0	0
Long-term debt	0
Subordinated notes	0	0
Total liabilities	2,631,378	1,939,954
Off-Balance-Sheet:
Commitments to extend credit	0	0
Fair Value [Member] | Level 2 [Member]
Assets:
Cash and short-term interest-earning assets	0	0
Held-to-maturity securities	24,871	41,061
Loans held for sale	5,943	4,708
Net loans and leases held for investment	0	0
Mortgage servicing rights	0	0
Other real estate owned		1,276
Total assets	30,814	47,045
Deposits:
Demand and savings deposits, non-maturity	0	0
Time deposits	628,096	455,527
Total deposits	628,096	455,527
Short-term borrowings	195,572	22,302
Long-term debt	130,157
Subordinated notes	95,188	50,375
Total liabilities	1,049,013	528,204
Off-Balance-Sheet:
Commitments to extend credit	(2,218)	(1,788)
Fair Value [Member] | Level 3 [Member]
Assets:
Cash and short-term interest-earning assets	0	0
Held-to-maturity securities	0	0
Loans held for sale	0	0
Net loans and leases held for investment	3,193,886	2,099,082
Mortgage servicing rights	9,548	8,047
Other real estate owned		0
Total assets	3,203,434	2,107,129
Deposits:
Demand and savings deposits, non-maturity	0	0
Time deposits	0	0
Total deposits	0	0
Short-term borrowings	0	0
Long-term debt	0
Subordinated notes	0	0
Total liabilities	0	0
Off-Balance-Sheet:
Commitments to extend credit	0	0
Carrying Amount [Member]
Assets:
Cash and short-term interest-earning assets	57,825	60,799
Held-to-maturity securities	24,881	40,990
Federal Home Loan Bank, Federal Reserve Bank and other stock	24,869	8,880
Loans held for sale	5,890	4,680
Net loans and leases held for investment	3,222,569	2,112,774
Mortgage servicing rights	6,485	5,877
Other real estate owned		1,276
Total assets	3,342,519	2,235,276
Deposits:
Demand and savings deposits, non-maturity	2,631,378	1,939,954
Time deposits	626,189	454,406
Total deposits	3,257,567	2,394,360
Short-term borrowings	196,171	24,211
Long-term debt	127,522
Subordinated notes	94,087	49,377
Total liabilities	3,675,347	2,467,948
Off-Balance-Sheet:
Commitments to extend credit	$ 0	$ 0