CONSOLIDATED CONDENSED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Preferred	Common Stock	Additional Paid in Capital	Retained Earnings	Accumulated Other Comprehensive Income
Beginning balance (in shares) at Dec. 31, 2017		125	49,158,238
Beginning balance at Dec. 31, 2017	$ 1,303,463	$ 125	$ 6,145	$ 834,870	$ 465,231	$ (2,908)
Comprehensive income:
Net income	76,313				76,313
Other comprehensive income (loss), net of tax	(21,334)					(21,334)
Cash dividends on common stock	(19,808)				(19,808)
Reclassification adjustment under ASU 2018-02	0				626	(626)
Share-based compensation (in shares)			98,021
Share-based compensation	1,653		$ 12	1,641
Stock issued under employee benefit plans (in shares)			9,205
Stock issued under employee benefit plans	344		$ 1	343
Stock issued under dividend reinvestment and stock purchase plan (in shares)			12,111
Stock issued under dividend reinvestment and stock purchase plan	555		$ 2	553
Stock options exercised (in shares)			44,932
Stock options exercised	953		$ 6	947
Stock redeemed (in shares)			(42,319)
Stock redeemed	(1,811)		$ (6)	(1,805)
Ending balance (in shares) at Jun. 30, 2018		125	49,280,188
Ending balance at Jun. 30, 2018	1,340,328	$ 125	$ 6,160	836,549	522,362	(24,868)
Beginning balance (in shares) at Mar. 31, 2018		125	49,243,096
Beginning balance at Mar. 31, 2018	1,313,073	$ 125	$ 6,155	834,894	493,624	(21,725)
Comprehensive income:
Net income	39,634				39,634
Other comprehensive income (loss), net of tax	(3,143)					(3,143)
Cash dividends on common stock	(10,896)				(10,896)
Share-based compensation (in shares)			4,945
Share-based compensation	776		$ 0	776
Stock issued under employee benefit plans (in shares)			4,842
Stock issued under employee benefit plans	187		$ 0	187
Stock issued under dividend reinvestment and stock purchase plan (in shares)			6,497
Stock issued under dividend reinvestment and stock purchase plan	305		$ 1	304
Stock options exercised (in shares)			21,375
Stock options exercised	418		$ 3	415
Stock redeemed (in shares)			(567)
Stock redeemed	(26)		$ 1	(27)
Ending balance (in shares) at Jun. 30, 2018		125	49,280,188
Ending balance at Jun. 30, 2018	1,340,328	$ 125	$ 6,160	836,549	522,362	(24,868)
Beginning balance (in shares) at Dec. 31, 2018		125	49,349,800
Beginning balance at Dec. 31, 2018	1,408,260	$ 125	$ 6,169	840,052	583,336	(21,422)
Comprehensive income:
Net income	79,873				79,873
Other comprehensive income (loss), net of tax	36,024					36,024
Cash dividends on common stock	(23,847)				(23,847)
Reclassification adjustment under ASU 2018-02						(626)
Share-based compensation (in shares)			108,638
Share-based compensation	1,825		$ 14	1,811
Stock issued under employee benefit plans (in shares)			11,247
Stock issued under employee benefit plans	362		$ 1	361
Stock issued under dividend reinvestment and stock purchase plan (in shares)			18,686
Stock issued under dividend reinvestment and stock purchase plan	$ 709		$ 2	707
Stock options exercised (in shares)	11,200		11,200
Stock options exercised	$ 105		$ 1	104
Stock redeemed (in shares)			(42,977)
Stock redeemed	(1,675)		$ (5)	(1,670)
Ending balance (in shares) at Jun. 30, 2019		125	49,456,594
Ending balance at Jun. 30, 2019	1,501,636	$ 125	$ 6,182	841,365	639,362	14,602
Beginning balance (in shares) at Mar. 31, 2019		125	49,428,468
Beginning balance at Mar. 31, 2019	1,455,848	$ 125	$ 6,179	839,919	611,220	(1,595)
Comprehensive income:
Net income	41,056				41,056
Other comprehensive income (loss), net of tax	16,197					16,197
Cash dividends on common stock	(12,914)				(12,914)
Share-based compensation (in shares)			4,978
Share-based compensation	844		$ 1	843
Stock issued under employee benefit plans (in shares)			5,908
Stock issued under employee benefit plans	188		$ 0	188
Stock issued under dividend reinvestment and stock purchase plan (in shares)			10,178
Stock issued under dividend reinvestment and stock purchase plan	369		$ 1	368
Stock options exercised (in shares)			7,500
Stock options exercised	65		$ 1	64
Stock redeemed (in shares)			(438)
Stock redeemed	(17)		$ 0	(17)
Ending balance (in shares) at Jun. 30, 2019		125	49,456,594
Ending balance at Jun. 30, 2019	$ 1,501,636	$ 125	$ 6,182	$ 841,365	$ 639,362	$ 14,602