Consolidated Statements of Changes in Shareholders' Equity - USD ($)	Total	Common stock and additional paid-in capital	Retained earnings	Accumulated other comprehensive income (loss)
Balance at Dec. 31, 2016	$ 172,521,000	$ 60,831,000	$ 111,693,000	$ (3,000)
Balance (in shares) at Dec. 31, 2016		10,793,946
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	19,588,000		19,588,000
Net unrealized loss on securities available for sale, net of tax	(1,452,000)			(1,452,000)
Net unrealized gain on cash flow hedging derivative instruments, net of tax	107,000			107,000
Net unrealized loss on securities transferred from available for sale to held to maturity, net of tax	(14,000)			(14,000)
Unrecognized gain (loss) for post-retirement benefits, net of tax	(19,000)			(19,000)
Comprehensive income	18,210,000		19,588,000	(1,378,000)
Cash dividends declared	(10,280,000)		(10,280,000)
Equity compensation expense	392,000	$ 392,000
Payment for repurchase of common stock	(154,000)		(154,000)
Payment for repurchase of common stock (in shares)		(5,562)
Reclassification adjustment for effect of enacted tax law changes	0		297,000	(297,000)
Issuance of restricted stock	0
Issuance of restricted stock (in shares)		18,850
Proceeds from sale of common stock	632,000	$ 632,000
Proceeds from sale of common stock (in shares)		22,684
Balance at Dec. 31, 2017	181,321,000	$ 61,855,000	121,144,000	(1,678,000)
Balance (in shares) at Dec. 31, 2017		10,829,918
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	5,506,000
Net unrealized loss on securities available for sale, net of tax	(3,309,000)
Net unrealized loss on securities transferred from available for sale to held to maturity, net of tax	(8,000)
Balance at Mar. 31, 2018	181,372,000
Balance at Dec. 31, 2017	181,321,000	$ 61,855,000	121,144,000	(1,678,000)
Balance (in shares) at Dec. 31, 2017		10,829,918
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	23,536,000		23,536,000
Net unrealized loss on securities available for sale, net of tax	(2,150,000)			(2,150,000)
Net unrealized gain on cash flow hedging derivative instruments, net of tax	(106,000)			(106,000)
Net unrealized loss on securities transferred from available for sale to held to maturity, net of tax	(23,000)			(23,000)
Unrecognized gain (loss) for post-retirement benefits, net of tax	184,000			184,000
Comprehensive income	21,441,000		23,536,000	(2,095,000)
Cash dividends declared	(12,052,000)		(12,052,000)
Equity compensation expense	381,000	$ 381,000
Payment for repurchase of common stock	(168,000)		(168,000)
Payment for repurchase of common stock (in shares)		(5,725)
Issuance of restricted stock	0
Issuance of restricted stock (in shares)		16,795
Proceeds from sale of common stock	619,000	$ 619,000
Proceeds from sale of common stock (in shares)		21,663
Balance at Dec. 31, 2018	$ 191,542,000	$ 62,855,000	132,460,000	(3,773,000)
Balance (in shares) at Dec. 31, 2018	10,862,651	10,862,651
Balance at Mar. 31, 2018	$ 181,372,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	5,734,000
Net unrealized loss on securities available for sale, net of tax	(1,035,000)
Net unrealized loss on securities transferred from available for sale to held to maturity, net of tax	(7,000)
Balance at Jun. 30, 2018	183,304,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	5,933,000
Net unrealized loss on securities available for sale, net of tax	(1,888,000)
Net unrealized loss on securities transferred from available for sale to held to maturity, net of tax	(5,000)
Balance at Sep. 30, 2018	184,661,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,363,000
Net unrealized loss on securities available for sale, net of tax	4,082,000
Net unrealized loss on securities transferred from available for sale to held to maturity, net of tax	(3,000)
Balance at Dec. 31, 2018	$ 191,542,000	$ 62,855,000	132,460,000	(3,773,000)
Balance (in shares) at Dec. 31, 2018	10,862,651	10,862,651
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 6,156,000
Net unrealized loss on securities available for sale, net of tax	3,512,000
Net unrealized loss on securities transferred from available for sale to held to maturity, net of tax	3,000
Balance at Mar. 31, 2019	197,787,000
Balance at Dec. 31, 2018	$ 191,542,000	$ 62,855,000	132,460,000	(3,773,000)
Balance (in shares) at Dec. 31, 2018	10,862,651	10,862,651
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 25,525,000		25,525,000
Net unrealized loss on securities available for sale, net of tax	8,708,000			8,708,000
Net unrealized gain on cash flow hedging derivative instruments, net of tax	(1,341,000)			(1,341,000)
Net unrealized loss on securities transferred from available for sale to held to maturity, net of tax	15,000			15,000
Unrecognized gain (loss) for post-retirement benefits, net of tax	(13,000)			(13,000)
Comprehensive income	32,894,000		25,525,000	7,369,000
Cash dividends declared	(12,963,000)		(12,963,000)
Equity compensation expense	565,000	$ 565,000
Payment for repurchase of common stock	(183,000)		(183,000)
Payment for repurchase of common stock (in shares)		(7,178)
Issuance of restricted stock	0
Issuance of restricted stock (in shares)		19,087
Proceeds from sale of common stock	653,000	$ 653,000
Proceeds from sale of common stock (in shares)		24,650
Balance at Dec. 31, 2019	$ 212,508,000	$ 64,073,000	144,839,000	3,596,000
Balance (in shares) at Dec. 31, 2019	10,899,210	10,899,210
Balance at Mar. 31, 2019	$ 197,787,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,395,000
Net unrealized loss on securities available for sale, net of tax	4,289,000
Net unrealized loss on securities transferred from available for sale to held to maturity, net of tax	4,000
Balance at Jun. 30, 2019	204,593,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,288,000
Net unrealized loss on securities available for sale, net of tax	936,000
Net unrealized loss on securities transferred from available for sale to held to maturity, net of tax	1,000
Balance at Sep. 30, 2019	208,489,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,686,000
Net unrealized loss on securities available for sale, net of tax	(29,000)
Net unrealized loss on securities transferred from available for sale to held to maturity, net of tax	7,000
Balance at Dec. 31, 2019	$ 212,508,000	$ 64,073,000	$ 144,839,000	$ 3,596,000
Balance (in shares) at Dec. 31, 2019	10,899,210	10,899,210