Taxes on Income, Earnings Before Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings (loss) before taxes on income [Abstract]
Earnings (loss) before taxes on income	$ (30,292)	$ 57,066	$ 44,854	$ 42,531	$ (58,860)	$ 47,861	$ 43,015	$ 40,998	$ 114,159	$ 73,014	$ 227,746
U.S. Federal [Abstract]
Current									0	11,143	28,919
Deferred									27,102	(258,703)	49,685
Total U.S. Federal									27,102	(247,560)	78,604
U.S. State [Abstract]
Current									(243)	3,861	4,727
Deferred									7,619	2,280	1,611
Total U.S. State									7,376	6,141	6,338
Foreign [Abstract]
Current									443	370	0
Deferred									160	160	0
Total Foreign									603	530	0
Consolidated [Abstract]
Current									200	15,374	33,646
Deferred									34,881	(256,263)	51,296
Total Provision (benefit) for taxes on income	$ (5,961)	$ 15,116	$ 16,061	$ 9,865	$ (290,357)	$ 19,072	$ 17,043	$ 13,353	35,081	(240,889)	84,942
United States [Member]
Earnings (loss) before taxes on income [Abstract]
Earnings (loss) before taxes on income									117,800	74,267	227,746
Foreign [Member]
Earnings (loss) before taxes on income [Abstract]
Earnings (loss) before taxes on income									$ (3,641)	$ (1,253)	$ 0