Taxes on Income (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Current deferred taxes:
Liabilities/expenses not currently deductible	$ 39,450	$ 43,902
Deferred equity compensation	7,175	8,149
Net operating losses		943
Total current deferred tax assets	46,625	52,994
Current deferred tax liabilities:
Earnings not currently taxable	(1,722)	(916)
Net current deferred tax assets	44,903	52,078
Non-current deferred tax assets:
Net operating losses	26,279	10,668
Deferred equity compensation	17,868	13,738
Liabilities/expenses not currently deductible	564	2,252
Total non-current deferred tax assets	44,711	26,658
Non-current deferred tax liabilities:
Property and equipment	(61,950)	(59,795)
Earnings not currently taxable	(10,673)	(9,158)
Total non-current deferred tax liabilities	(72,623)	(68,953)
Net non-current deferred tax liabilities	$ (27,912)	$ (42,295)