Income Taxes - Deferred tax assets (liabilities) (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Accrued expenses	$ 2,463,000	$ 2,839,000	$ 1,717,000
Net operating loss	4,834,000	3,977,000	5,192,000
Allowance for loan losses, net of bad debt charge-offs	8,400,000	8,061,000	6,252,000
Deferred compensation	3,074,000	2,348,000	2,547,000
State taxes	1,500,000	1,879,000	1,451,000
Depreciation	0	1,090,000	651,000
Loan discount	8,642,000	3,477,000	0
Stock-based compensation	1,914,000	1,108,000	639,000
Unrealized loss on available for sale securities	0	1,939,000	0
Capital loss carryover	380,000	0	0
AMT credit	107,000	0	0
Total deferred tax assets	31,314,000	26,718,000	18,449,000
Deferred tax liabilities:
Deferred FDIC gain	(524,000)	(1,675,000)	(1,656,000)
Core deposit intangibles	(11,691,000)	(3,331,000)	(2,266,000)
Loan origination costs	(3,368,000)	(4,208,000)	0
Depreciation	(699,000)	0	0
Unrealized loss on available for sale securities	(188,000)	0	(231,000)
Other	(1,199,000)	(697,000)	(2,785,000)
Total deferred tax liabilities	(17,669,000)	(9,911,000)	(6,938,000)
Valuation allowance	(380,000)	0	0
Net deferred tax asset	$ 13,265,000	$ 16,807,000	$ 11,511,000