Share Capital and Capital In Excess of Par Value (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Changes in share capital and capital in excess of par value
Balance at the beginning of the period			$ 768,797
Balance at the beginning of the period (in shares)			96
Purchase and retirement of common shares			$ (8,024)	$ (30,184)
Purchase and retirement of common shares (in shares)			(230)	(921)
Balance at the end of the period	$ 783,323	$ 756,516	$ 783,323	$ 756,516
Balance at the end of the period (in shares)	99	96	99	96
Stock dividends (as a percent)	3.00%	3.00%	3.00%	3.00%
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)	$ (1,992)
Balance at the beginning of the period (in shares)	99	96	96	93
Issuance of 3% stock dividend (in shares)			3	3
Balance at the end of the period	$ (1,992)	$ (1,992)	$ (1,992)	$ (1,992)
Balance at the end of the period (in shares)	99	96	99	96
Capital in Excess of Par Value
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 746,026	$ 722,617	$ 709,880	$ 706,930
Issuance of 3% stock dividend			41,068	32,495
Purchase and retirement of common shares	(2,942)	(12,737)	(7,864)	(29,545)
Balance at the end of the period	743,084	709,880	743,084	709,880
Class B Common Stock | Common Stock.
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 19,877	$ 19,320	$ 19,300	$ 18,758
Balance at the beginning of the period (in shares)	28,623	27,821	27,793	27,012
Issuance of 3% stock dividend			$ 579	$ 562
Issuance of 3% stock dividend (in shares)			833	809
Conversion of Class B common shares to common shares		$ (11)	$ (3)	$ (11)
Conversion of Class B common shares to common shares (in shares)		(16)	(4)	(16)
Purchase and retirement of common shares			$ 1
Purchase and retirement of common shares (in shares)	(1)
Balance at the end of the period	$ 19,877	$ 19,309	$ 19,877	$ 19,309
Balance at the end of the period (in shares)	28,622	27,805	28,622	27,805
Common Stock | Common Stock.
Changes in share capital and capital in excess of par value
Balance at the beginning of the period	$ 28,041	$ 27,569	$ 27,322	$ 27,134
Balance at the beginning of the period (in shares)	40,379	39,700	39,344	39,073
Issuance of 3% stock dividend			$ 817	$ 808
Issuance of 3% stock dividend (in shares)			1,176	1,163
Conversion of Class B common shares to common shares		$ 11	$ 3	$ 11
Conversion of Class B common shares to common shares (in shares)		16	4	16
Purchase and retirement of common shares	$ (59)	$ (266)	$ (160)	$ (639)
Purchase and retirement of common shares (in shares)	(85)	(384)	(230)	(920)
Balance at the end of the period	$ 27,982	$ 27,314	$ 27,982	$ 27,314
Balance at the end of the period (in shares)	40,294	39,332	40,294	39,332