Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	COMMON STOCK [Member]	CAPITAL SURPLUS [Member]	RETAINED EARNINGS [Member]	RETAINED EARNINGS [Member] CUMULATIVE EFFECT, PERIOD OF ADOPTION, ADJUSTMENT [Member]	ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) [Member]
Balance at beginning of period at Dec. 31, 2019		$ 32,694	$ 153,353	$ 815,488	$ 2,270	$ 3,454
Shares issued for stock options		12	220
Shares acquired and canceled		(59)		(3,039)
Net income	$ 22,608			$ 22,608
Accounting Standards Update Extensible List				us-gaap:AccountingStandardsUpdate201613Member
Dividends on common stock				$ (10,472)
Stock-based compensation arrangements			426
Net change						6,425
Balance at end of period at Mar. 31, 2020	1,023,380	32,647	153,999	826,855		9,879
Balance at beginning of period at Dec. 31, 2020	1,067,885	32,720	156,574	871,161		7,430
Shares issued for stock options		51	1,258
Net income	42,520			42,520
Dividends on common stock				(11,134)
Net cash settlement of options			(958)	(4,521)
Stock-based compensation arrangements			576
Net change						(1,006)
Balance at end of period at Mar. 31, 2021	$ 1,094,671	$ 32,771	$ 157,450	$ 898,026		$ 6,424