Pension Plans and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Qualified Defined Contribution Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions to employees' accounts	$ 0	$ 4,580	$ 4,616
Total assets at the end of the year	9,088	123,008	135,097
401 K Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions to employees' accounts	6,466	2,753	2,781
Total assets at the end of the year	161,956	132,053	134,897
Non Qualified Defined Contribution Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions to employees' accounts	122	74	110
Total assets at the end of the year	$ 0	$ 0	$ 0