Condensed Financial Information of Parent Company (Schedule of Condensed Statement 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
Income from subsidiaries:
Net interest income after provision										$ 39,790		$ 39,401	$ 37,449
Gain on sales of investment securities												387	2,910
Total net revenue										135,302		125,537	120,817
Expenses:
Salaries and employee benefits										77,339		72,581	70,314
Other expenses										1,722		1,913	1,185
Total operating expense	$ 26,142		$ 25,042	$ 24,901	$ 24,318	$ 23,946	$ 23,552	$ 23,059	$ 22,916	100,403		93,473	89,783
Income tax expense	3,576	[1]	2,396	2,248	1,665	1,806	1,855	2,035	2,020	9,885	[1]	7,716	7,978
Net income	$ 5,331		$ 6,863	$ 6,513	$ 6,307	$ 6,424	$ 6,222	$ 5,869	$ 5,833	25,014		24,348	23,056
Parent Company [Member]
Income from subsidiaries:
Interest												2	12
Management fees										2,172		2,105	2,201
Income from subsidiaries										2,172		2,107	2,213
Information services revenue										93,133		83,543	78,488
Net interest income after provision										13,217		13,389	13,948
Gain on sales of investment securities												387	2,910
Other income										483		504	613
Total net revenue										109,005		99,930	98,172
Expenses:
Salaries and employee benefits										70,409		65,968	63,475
Other expenses										20,333		18,133	16,580
Total operating expense										90,742		84,101	80,055
Income before income tax and equity in undistributed income of subsidiaries										18,263		15,829	18,117
Income tax expense										4,394		1,540	2,950
Income before undistributed income of subsidiaries										13,869		14,289	15,167
Equity in undistributed income of subsidiaries										11,145		10,059	7,889
Net income										$ 25,014		$ 24,348	$ 23,056

[1] Includes one-time, non-cash TCJA charge of $1,824,000