Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other assets — other notes and accounts receivable
Reserves deducted from asset accounts:
Balance at Beginning of Year	$ 159	$ 775	$ 1,043
Additions (Reductions) Charged to Costs and Expenses	7,683	0	346
Charged to Other Accounts	0	0	0
Deductions	0	616	614
Balance at End of Year	7,842	159	775
Current assets — supplies and inventory
Reserves deducted from asset accounts:
Balance at Beginning of Year	6,625	8,446	12,589
Additions (Reductions) Charged to Costs and Expenses	431	580	503
Charged to Other Accounts	0	(76)	(2,274)
Deductions	1,065	2,325	2,372
Balance at End of Year	5,991	6,625	8,446
Deferred income taxes
Reserves deducted from asset accounts:
Balance at Beginning of Year	270,251	43,322	34,663
Additions (Reductions) Charged to Costs and Expenses	860,847	226,929	8,659
Charged to Other Accounts	0	0	0
Deductions	0	0	0
Balance at End of Year	$ 1,131,098	$ 270,251	$ 43,322