Consolidated Statement of Changes in Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2017	$ 425,423	$ 204	$ 210,081	$ (22,370)	$ 233,896	$ 3,612
Beginning Balance, Shares at Dec. 31, 2017		20,504,165
Treasury Stock Beginning Balance, Shares at Dec. 31, 2017				(1,258,250)
Comprehensive income:
Impact of adoption of ASU | ASU 2016-01 [Member]	614				614
Impact of adoption of ASU | ASU 2018-02 [Member]	(414)				(414)
Net income	33,125				33,125
Other comprehensive income:
Change in unrealized gains (losses), net of tax	(5,695)					(5,695)
Comprehensive income	27,430
Common stock issued upon exercise of options	$ 67		67
Common stock issued upon exercise of options, Shares	15,000	15,000
Common stock issued	$ 196	$ 1	195
Common stock issued, Shares		9,065
Share-based compensation	552		552
Dividends to shareholders	(8,477)				(8,477)
Ending Balance at Jun. 30, 2018	445,391	$ 205	210,895	$ (22,370)	258,744	(2,083)
Ending Balance, Shares at Jun. 30, 2018		20,528,230
Treasury Stock Ending Balance, Shares at Jun. 30, 2018				(1,258,250)
Beginning Balance at Mar. 31, 2018	432,068	$ 205	210,441	$ (22,370)	246,028	(2,236)
Beginning Balance, Shares at Mar. 31, 2018		20,519,165
Treasury Stock Beginning Balance, Shares at Mar. 31, 2018				(1,258,250)
Comprehensive income:
Impact of adoption of ASU | ASU 2016-01 [Member]	(1)				(1)
Net income	16,956				16,956
Other comprehensive income:
Change in unrealized gains (losses), net of tax	153					153
Comprehensive income	17,109
Common stock issued upon exercise of options	(1)	$ (1)
Common stock issued	196	$ 1	195
Common stock issued, Shares		9,065
Share-based compensation	259		259
Dividends to shareholders	(4,239)				(4,239)
Ending Balance at Jun. 30, 2018	445,391	$ 205	210,895	$ (22,370)	258,744	(2,083)
Ending Balance, Shares at Jun. 30, 2018		20,528,230
Treasury Stock Ending Balance, Shares at Jun. 30, 2018				(1,258,250)
Beginning Balance at Dec. 31, 2018	$ 409,762	$ 205	211,431	$ (22,370)	221,328	(832)
Beginning Balance, Shares at Dec. 31, 2018	20,528,230	20,528,230
Treasury Stock Beginning Balance, Shares at Dec. 31, 2018	(1,258,250)			(1,258,250)
Comprehensive income:
Impact of adoption of ASU | ASU 2016-02 [Member]	$ (1)				(1)
Net income	37,290				37,290
Other comprehensive income:
Change in unrealized gains (losses), net of tax	10,972					10,972
Comprehensive income	48,262
Common stock issued upon exercise of options	$ 20		20
Common stock issued upon exercise of options, Shares	5,000	5,000
Common stock issued	$ 560		560
Common stock issued, Shares		23,281
Share-based compensation	482		482
Dividends to shareholders	(9,642)				(9,642)
Ending Balance at Jun. 30, 2019	$ 449,443	$ 205	212,493	$ (22,370)	248,975	10,140
Ending Balance, Shares at Jun. 30, 2019	20,556,511	20,556,511
Treasury Stock Ending Balance, Shares at Jun. 30, 2019	(1,258,250)			(1,258,250)
Beginning Balance at Mar. 31, 2019	$ 430,405	$ 205	211,700	$ (22,370)	235,908	4,962
Beginning Balance, Shares at Mar. 31, 2019		20,533,230
Treasury Stock Beginning Balance, Shares at Mar. 31, 2019				(1,258,250)
Comprehensive income:
Net income	17,890				17,890
Other comprehensive income:
Change in unrealized gains (losses), net of tax	4,980					4,980
Change in deferred tax valuation allowance	198					198
Comprehensive income	23,068
Common stock issued	560		560
Common stock issued, Shares		23,281
Share-based compensation	233		233
Dividends to shareholders	(4,823)				(4,823)
Ending Balance at Jun. 30, 2019	$ 449,443	$ 205	$ 212,493	$ (22,370)	$ 248,975	$ 10,140
Ending Balance, Shares at Jun. 30, 2019	20,556,511	20,556,511
Treasury Stock Ending Balance, Shares at Jun. 30, 2019	(1,258,250)			(1,258,250)