Taxes on Income, Earnings Before Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Line Items]
Earnings (loss) before taxes on income	$ (58,860)	$ 47,861	$ 43,015	$ 40,998	$ 52,370	$ 51,559	$ 62,474	$ 61,343		$ 73,014	$ 227,746	$ 361,712
U.S. Federal [Abstract]
Current										11,143	28,919	64,707
Deferred										(258,703)	49,685	59,582
Total U.S. Federal										(247,560)	78,604	124,289
U.S. State [Abstract]
Current										3,861	4,727	6,280
Deferred										2,280	1,611	3,173
Total U.S. State										6,141	6,338	9,453
Foreign [Abstract]
Current										370	0	0
Deferred										160	0	0
Total Foreign										530	0	0
Consolidated [Abstract]
Current										15,374	33,646	70,987
Deferred										(256,263)	51,296	62,755
Total Provision (benefit) for taxes on income	$ (290,357)	$ 19,072	$ 17,043	$ 13,353	$ 19,512	$ 19,206	$ 23,365	$ 22,859		$ (240,889)	$ 84,942	$ 133,742
Effective income tax rate										35.00%	35.00%	35.00%
One-time deferred tax benefit										$ (269,472)
Plan [Member]
Consolidated [Abstract]
Effective income tax rate									21.00%
United States [Member]
Income Tax Disclosure [Line Items]
Earnings (loss) before taxes on income										74,267	$ 227,746	$ 361,712
Foreign [Member]
Income Tax Disclosure [Line Items]
Earnings (loss) before taxes on income										$ (1,253)	$ 0	$ 0