Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017		Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive (loss) income	$ (888)	$ (2,575)	$ 1,732	[1]	$ (3,262)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(2,064)	650
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(556)	37
Other Comprehensive Income (Loss), Net of Tax	(2,620)	687
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive (loss) income	398	0	398		0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Other Comprehensive Income (Loss), Net of Tax	0	0
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive (loss) income	(849)	(2,409)	(1,564)		(2,906)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	715	497
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0	0
Other Comprehensive Income (Loss), Net of Tax	715	497
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive (loss) income	(437)	(166)	$ 2,898		$ (356)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(2,779)	153
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(556)	37
Other Comprehensive Income (Loss), Net of Tax	$ (3,335)	$ 190

[1] Derived from audited consolidated financial statements