Parent Company Only Financial Statements Condensed statements of income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Income before income taxes	$ 9,122	$ 11,133	$ 12,127	$ 9,344	$ 10,660	$ 8,120	$ 7,553	$ 7,447	$ 41,726	$ 33,780	$ 25,730
Income tax benefit	(4,497)	(3,538)	(3,927)	(3,080)	(3,863)	(2,812)	(2,624)	(2,641)	(15,042)	(11,940)	(9,218)
Net income available to common stockholders	$ 4,625	$ 7,595	$ 8,200	$ 6,264	$ 6,797	$ 5,308	$ 4,654	$ 4,256	26,684	21,015	14,312
Other Comprehensive Income (Loss), Net of Tax									3,525	(6,484)	1,598
Comprehensive income									30,209	15,356	18,110
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Dividends from subsidiaries									18,925	19,475	6,094
Other income									1,227	66	66
Total income									20,152	19,541	6,160
Operating expenses									3,902	3,491	2,556
Income before income taxes									16,250	16,050	3,604
Income tax benefit									864	1,073	974
Income before equity in undistributed earnings of subsidiaries									17,114	17,123	4,578
Equity in undistributed earnings of subsidiaries									9,570	4,717	11,934
Net income available to common stockholders									26,684	21,840	16,512
Other Comprehensive Income (Loss), Net of Tax									3,525	(6,484)	1,598
Comprehensive income									$ 30,209	$ 15,356	$ 18,110