Accumulated Other Comprehensive Income (Loss), Accumulated Other Comprehensive Income (Loss) Reclassifications (Details) - Unrealized Gain (Loss) on Available-for-Sale Securities [Member] - Reclassification out of Accumulated Other Comprehensive Income [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Rabbi Trust Assets [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Component of Selling, General, and Administrative Expense	$ 817	$ 0	$ 680
Other AFS Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Component of Other Income	$ 0	$ 0	$ 0