Employee Benefit Plans - Expected long-term return by asset category (Details)	12 Months Ended
	Dec. 31, 2014
Expected Long Term Return [Abstract]
Expected long-term return	5.20%
Assets allocation [Abstract]
Assets allocation	100.00%
Gilt Securities
Expected Long Term Return [Abstract]
Expected long-term return	2.40%
Assets allocation [Abstract]
Assets allocation	19.00%
Cash
Expected Long Term Return [Abstract]
Expected long-term return	0.50%
Assets allocation [Abstract]
Assets allocation	2.00%
Equity Securities
Expected Long Term Return [Abstract]
Expected long-term return	7.20%
Assets allocation [Abstract]
Assets allocation	42.00%
Corporate Bond Securities
Expected Long Term Return [Abstract]
Expected long-term return	3.40%
Assets allocation [Abstract]
Assets allocation	25.00%
Target Return Funds
Expected Long Term Return [Abstract]
Expected long-term return	7.20%
Assets allocation [Abstract]
Assets allocation	12.00%