Parent Company Financial Information (Condensed Statements of Income) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Expenses:
Salaries									$ 1,890,000
Other operating expenses									11,949,000	$ 11,755,000	$ 11,966,000
Total noninterest expense	$ 16,723,000	$ 14,330,000	$ 14,776,000	$ 15,135,000	$ 15,089,000	$ 14,242,000	$ 15,707,000	$ 14,868,000	60,964,000	59,906,000	54,852,000
Income before income taxes	10,839,000	12,970,000	12,798,000	13,176,000	11,921,000	10,592,000	12,054,000	12,068,000	49,783,000	46,635,000	45,011,000
Income tax benefit	1,652,000	2,187,000	2,054,000	2,335,000	1,831,000	535,000	1,739,000	957,000	8,228,000	5,062,000	9,889,000
Net income	9,187,000	10,783,000	10,744,000	10,841,000	10,090,000	10,057,000	10,315,000	11,111,000	41,555,000	41,573,000	35,122,000
Comprehensive income	$ 10,577,000	$ 11,246,000	$ 14,064,000	$ 15,703,000	$ 12,118,000	$ 8,952,000	$ 7,869,000	$ 2,925,000	51,590,000	31,864,000	37,272,000
Parent Company [Member]
Income:
Dividends from subsidiary bank									55,750,000	15,525,000	11,150,000
Expenses:
Salaries									3,050,000	1,814,000	2,434,000
Other operating expenses									442,000	343,000	406,000
Total noninterest expense									3,492,000	2,157,000	2,840,000
Income before income taxes									52,258,000	13,368,000	8,310,000
Income tax benefit									(755,000)	(1,442,000)	(1,235,000)
Income before undistributed earnings of subsidiary bank									53,013,000	14,810,000	9,545,000
Equity in undistributed earnings									(11,458,000)	26,763,000	25,577,000
Net income									41,555,000	41,573,000	35,122,000
Comprehensive income									$ 51,590,000	$ 31,864,000	$ 37,272,000