Condensed Consolidated Statements of Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Parent [Member]	Noncontrolling Interest [Member]	Total
Balance (in shares) at Dec. 31, 2017	50,609
Balance at Dec. 31, 2017	$ 51	$ 888,778	$ 327,255	$ (4,706)	$ 1,211,378	$ 84,322	$ 1,295,700
Cumulative effect of changes in accounting principles at Dec. 31, 2017			25,635		25,635		25,635
Adjusted balance as of the beginning of the year at Dec. 31, 2017	51	888,778	352,890	(4,706)	1,237,013	84,322	1,321,335
Stock-based compensation		1,707			1,707		1,707
Exercise of options by employees and directors (in shares)	8
Exercise of options by employees and directors
Cash paid to noncontrolling interest						(4,674)	(4,674)
Cash dividend declared			(11,640)		(11,640)		(11,640)
Net income			69,508		69,508	4,482	73,990
Currency translation adjustment				1,158	1,158	370	1,528
Loss in respect of derivative instruments designated for cash flow hedge				20	20		20
Change in unrealized gains or losses in respect of the Company's share in derivative instruments of unconsolidated investment				2,634	2,634		2,634
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge				(15)	(15)		(15)
Balance (in shares) at Mar. 31, 2018	50,617
Balance at Mar. 31, 2018	$ 51	890,485	410,758	(909)	1,300,385	84,500	1,384,885
Balance (in shares) at Dec. 31, 2018	50,700
Balance at Dec. 31, 2018	$ 51	901,363	422,222	(3,799)	1,319,837	125,259	1,445,096
Cumulative effect of changes in accounting principles at Dec. 31, 2018			(58)		(58)		(58)
Adjusted balance as of the beginning of the year at Dec. 31, 2018	51	901,363	422,164	(3,799)	1,319,779	125,259	1,445,038
Stock-based compensation		2,360			2,360		2,360
Exercise of options by employees and directors (in shares)	52
Exercise of options by employees and directors
Cash paid to noncontrolling interest						(4,146)	(4,146)
Cash dividend declared			(5,579)		(5,579)		(5,579)
Net income			25,946		25,946	1,855	27,801
Currency translation adjustment				(1,026)	(1,026)	(322)	(1,348)
Loss in respect of derivative instruments designated for cash flow hedge				22	22		22
Change in unrealized gains or losses in respect of the Company's share in derivative instruments of unconsolidated investment				(1,145)	(1,145)		(1,145)
Amortization of unrealized gains in respect of derivative instruments designated for cash flow hedge				(8)	(8)		(8)
Balance (in shares) at Mar. 31, 2019	50,752
Balance at Mar. 31, 2019	$ 51	$ 903,723	$ 442,531	$ (5,956)	$ 1,340,349	$ 122,646	$ 1,462,995