Unconditional Purchase Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Unconditional Purchase Obligations (Excluding Capital Stock Redemptions) [Abstract]
Unconditional purchase obligations, beginning of year	$ 5,300	$ 2,900	$ 3,300
Future expenditures under purchase obligations, next twelve months	7,199
Future expenditures under purchase obligations, year two	1,301
Future expenditures under purchase obligations, year three	$ 688