Income Taxes - Deferred tax assets (liabilities) (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Accrued expenses	$ 3,239,000	$ 2,463,000	$ 2,839,000
Net operating loss	6,115,000	4,834,000	3,977,000
Allowance for loan losses, net of bad debt charge-offs	10,709,000	8,400,000	8,061,000
Deferred compensation	3,649,000	3,074,000	2,348,000
State taxes	2,707,000	1,500,000	1,879,000
Depreciation	0	0	1,090,000
Loan discount	17,677,000	8,642,000	3,477,000
Stock-based compensation	3,234,000	1,914,000	1,108,000
Unrealized loss on available for sale securities	2,308,000	0	1,939,000
Capital loss carryover	0	380,000	0
AMT credit	96,000	107,000	0
Total deferred tax assets	49,734,000	31,314,000	26,718,000
Deferred tax liabilities:
Deferred FDIC gain	(364,000)	(524,000)	(1,675,000)
Core deposit intangibles	(27,388,000)	(11,691,000)	(3,331,000)
Loan origination costs	(4,760,000)	(3,368,000)	(4,208,000)
Depreciation	(1,192,000)	(699,000)	0
Unrealized gain on available for sale securities	0	(188,000)	0
Other	(403,000)	(1,199,000)	(697,000)
Total deferred tax liabilities	(34,107,000)	(17,669,000)	(9,911,000)
Valuation allowance	0	(380,000)	0
Net deferred tax asset	$ 15,627,000	$ 13,265,000	$ 16,807,000