Supplemental Comprehensive Income Disclosures (Details 2) - 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 Income (Loss), Beginning Balance	$ (6,173)
Other comprehensive income (loss) before reclassification adjustment	(3,145)	$ 1,653
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	(103)	(335)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	0	(50)
Total other comprehensive (loss) income	(5,492)	944
Accumulated Other Comprehensive Income (Loss), Ending Balance	(13,009)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(7,510)	(7,455)
Other comprehensive income (loss) before reclassification adjustment	(3,145)	1,653
Amounts reclassified from accumulated other comprehensive income (loss)	(2,244)	(424)
Total other comprehensive (loss) income	(5,389)	1,229
Accumulated Other Comprehensive Income (Loss), Ending Balance	(12,899)	(6,226)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	299	225
Other comprehensive income (loss) before reclassification adjustment	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Total other comprehensive (loss) income	0	0
Accumulated Other Comprehensive Income (Loss), Ending Balance	299	225
Derivative [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(306)	203
Total other comprehensive (loss) income	(103)	(285)
Accumulated Other Comprehensive Income (Loss), Ending Balance	(409)	(82)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(7,517)	(7,027)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(3,248)	1,318
Amounts reclassified from accumulated other comprehensive income (loss)	(2,244)	(374)
Total other comprehensive (loss) income	(5,492)	944
Accumulated Other Comprehensive Income (Loss), Ending Balance	(13,009)	(6,083)
Scenario, Previously Reported [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(6,166)	(7,455)
Scenario, Previously Reported [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	299	225
Scenario, Previously Reported [Member] | Derivative [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	(306)	203
Scenario, Previously Reported [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (6,173)	$ (7,027)
Effect of ASU Adoption [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			$ 0	$ 0
Effect of ASU Adoption [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			(1,344)	0
Effect of ASU Adoption [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			0	0
Effect of ASU Adoption [Member] | Derivative [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			0
Effect of ASU Adoption [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			$ (1,344)	$ 0