CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - UNAUDITED - USD ($) $ in Thousands	Total	Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Common sttock	Common sttock Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Retained Earnings [Member]	Retained Earnings [Member] Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Revision of Prior Period, Accounting Standards Update, Adjustment [Member]
Balance at at Dec. 31, 2018	$ 1,067,903		$ 35,531		$ 606,573		$ 441,553		$ (15,754)
Net income	30,317		0		0		30,317		0
Other comprehensive income, net of tax	6,704		0		0		0		6,704
Common stock dividends - $0.30 and $0.28 per share for the first quarter ended: March 31, 2020 and 2019 respectively	(10,008)		0		0		(10,008)		0
Stock compensation expense	690		0		690		0		0
Common stock issued pursuant to:
Stock option plan 6,013 and 6,755 shares for the quarters ended: March 2020, 2019 respectively	129		7		122		0		0
Employee stock purchase plan - 8,617 and 7,662 shares for the quarters ended: March 2020, 2019 respectively	214		7		207		0		0
Restricted stock - 11,959 shares for the quarter ended: March 31, 2019	(101)		12		(113)		0		0
Balance at at Mar. 31, 2019	1,095,848		35,557		607,479		461,862		(9,050)
Balance at at Dec. 31, 2019	1,132,974		34,970		586,622		515,714		(4,332)
Net income	9,987		0		0		9,987		0
Other comprehensive income, net of tax	10,676		0		0		0		10,676
Common stock dividends - $0.30 and $0.28 per share for the first quarter ended: March 31, 2020 and 2019 respectively	(10,544)		0		0		(10,544)		0
Stock compensation expense	754		0		754		0		0
Common stock issued pursuant to:
Stock option plan 6,013 and 6,755 shares for the quarters ended: March 2020, 2019 respectively	122		6		116		0		0
Employee stock purchase plan - 8,617 and 7,662 shares for the quarters ended: March 2020, 2019 respectively	290		9		281		0		0
Adoption of ASC 326 - Financial Instruments - Credit Losses		$ (2,223)		$ 0		$ 0		$ (2,223)		$ 0
Purchase of treasury shares - 820,328 shares	(25,702)		(820)		(24,882)		0		0
Balance at at Mar. 31, 2020	$ 1,116,334		$ 34,165		$ 562,891		$ 512,934		$ 6,344
Common stock issued pursuant to:
Accounting Standards Update [Extensible List]	u-sgaap:AccountingStandardsUpdate201613Member