Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	CUMULATIVE EFFECT, PERIOD OF ADOPTION, ADJUSTMENT [Member]	Common Stock [Member]	CAPITAL SURPLUS [Member]	RETAINED EARNINGS [Member]	RETAINED EARNINGS [Member] CUMULATIVE EFFECT, PERIOD OF ADOPTION, ADJUSTMENT [Member]	ACCUMULATED OTHER COMPREHENSIVE INCOME [Member]
Balance at beginning of period, Shares at Dec. 31, 2018			32,603,926
Balance at beginning of period at Dec. 31, 2018			$ 32,604	$ 149,709	$ 722,615		$ (2,139)
Shares issued for stock options, Shares			117,012
Shares issued for stock options, Value			$ 117	2,367
Net income	$ 134,879				134,879
Net change							5,593
Dividends on common stock					(40,432)
Stock-based compensation arrangements				1,277
Shares acquired and canceled, Shares			(26,670)
Shares acquired and canceled, Value			$ (27)		(1,574)
Balance at end of period, Shares at Dec. 31, 2019	32,694,268		32,694,268
Balance at end of period at Dec. 31, 2019	$ 1,004,989		$ 32,694	153,353	815,488	$ 2,270	3,454
Accounting Standards Update Extensible List		ASC 326 [Member]				ASC 326 [Member]
Shares issued for stock options, Shares			84,868
Shares issued for stock options, Value			$ 85	1,705
Net income	$ 99,586				99,586
Net change							3,976
Dividends on common stock					(43,144)
Stock-based compensation arrangements				1,516
Shares acquired and canceled, Shares			(59,284)
Shares acquired and canceled, Value			$ (59)		(3,039)
Balance at end of period, Shares at Dec. 31, 2020	32,719,852		32,719,852
Balance at end of period at Dec. 31, 2020	$ 1,067,885		$ 32,720	156,574	871,161		7,430
Shares issued for stock options, Shares			95,562
Shares issued for stock options, Value			$ 95	2,165
Net income	$ 167,630				167,630
Net change							(5,280)
Dividends on common stock					(45,752)
Net cash settlement of options				(958)	(4,521)
Stock-based compensation arrangements				2,133
Shares acquired and canceled, Shares			(212,296)
Shares acquired and canceled, Value			$ (212)		(11,451)
Balance at end of period, Shares at Dec. 31, 2021	32,603,118		32,603,118
Balance at end of period at Dec. 31, 2021	$ 1,171,734		$ 32,603	$ 159,914	$ 977,067		$ 2,150