Parent company only financial statements - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
ASSETS
Cash and cash equivalents	$ 125,356	$ 119,751	$ 136,327	$ 97,723
Other assets	70,102	44,216
Goodwill	137,190	137,190	46,867
Total assets	5,136,764	4,727,713	3,276,881
LIABILITIES
Accrued expenses and other liabilities	65,414	118,994
Total liabilities	4,464,907	4,130,984
SHAREHOLDERS' EQUITY
Common stock	30,725	30,536
Additional paid-in capital	424,146	418,596
Retained earnings	221,213	147,449
Accumulated other comprehensive (loss) income	(4,227)	148
Total shareholders' equity	671,857	596,729	330,498	236,674
Total liabilities and shareholders' equity	5,136,764	4,727,713
Parent Company
ASSETS
Cash and cash equivalents	17,400	25,789	$ 30,993	$ 1,253
Investments	0	1,129
Investments in Bank subsidiary	679,097	595,625
Other assets	7,364	5,411
Goodwill	29	29
Total assets	703,890	627,983
LIABILITIES
Borrowings	30,930	30,930
Accrued expenses and other liabilities	1,103	324
Total liabilities	32,033	31,254
SHAREHOLDERS' EQUITY
Common stock	30,725	30,536
Additional paid-in capital	424,146	418,596
Retained earnings	221,213	147,449
Accumulated other comprehensive (loss) income	(4,227)	148
Total shareholders' equity	671,857	596,729
Total liabilities and shareholders' equity	$ 703,890	$ 627,983