SHARE CAPITAL AND CAPITAL IN EXCESS OF PAR VALUE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 763,100
Balance at the beginning of the period (in shares)	93
Balance at the end of the period	$ 768,797	$ 763,100
Balance at the end of the period (in shares)	96	93
Total Number of Shares Purchased	921	982	923
Average Price Paid Per Share (in dollars per share)	$ 32.76	$ 32.59	$ 36.93
Stock dividends (as a percent)	3.00%	3.00%	3.00%
Common Stock.
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 27,134	$ 26,969	$ 26,767
Balance at the beginning of the period (in shares)	39,073	38,836	38,544
Issuance of 3% stock dividend	$ 807	$ 804	$ 798
Issuance of 3% stock dividend (in shares)	1,163	1,157	1,150
Conversion of Class B common shares to common shares	$ 20	$ 43	$ 45
Conversion of Class B common shares to common shares (in shares)	29	62	65
Purchase and retirement of common shares	$ (639)	$ (682)	$ (641)
Purchase and retirement of common shares (in shares)	(921)	(982)	(923)
Balance at the end of the period	$ 27,322	$ 27,134	$ 26,969
Balance at the end of the period (in shares)	39,344	39,073	38,836
Treasury Stock
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ (1,992)	$ (1,992)	$ (1,992)
Balance at the beginning of the period (in shares)	93	90	88
Issuance of 3% stock dividend (in shares)	3	3	2
Balance at the end of the period	$ (1,992)	$ (1,992)	$ (1,992)
Balance at the end of the period (in shares)	96	93	90
Capital in Excess of Par Value
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 706,930	$ 696,059	$ 696,535
Issuance of 3% stock dividend	32,495	42,244	32,999
Purchase and retirement of common shares	(29,545)	(31,373)	(33,475)
Balance at the end of the period	709,880	706,930	696,059
Class B Common Stock | Common Stock.
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 18,758	$ 18,254	$ 17,767
Balance at the beginning of the period (in shares)	27,012	26,287	25,584
Issuance of 3% stock dividend	$ 562	$ 547	$ 532
Issuance of 3% stock dividend (in shares)	810	787	768
Conversion of Class B common shares to common shares	$ (20)	$ (43)	$ (45)
Conversion of Class B common shares to common shares (in shares)	(29)	(62)	(65)
Balance at the end of the period	$ 19,300	$ 18,758	$ 18,254
Balance at the end of the period (in shares)	27,793	27,012	26,287