Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019	Jan. 01, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance			$ (38,784)
Accumulated Other Comprehensive Income (Loss), ending balance	$ (35,693)		(35,693)		$ (35,693)
Accumulated Defined Benefit Plans Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets							$ 0	$ 0
Accumulated Net Unrealized Investment Gain (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets							0	(41,028)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets							0	0
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets							$ 0	$ (41,028)
Accumulated Defined Benefit Plans Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	(26,001)	$ (18,475)	(24,923)	$ (17,790)	(19,124)	$ (24,915)
Other Comprehensive Income (Loss) before Reclassifications	0	0	0	0	(4,589)	7,951
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(1,023)	(649)	(2,101)	(1,334)	(3,311)	(2,160)
Accumulated Other Comprehensive Income (Loss), ending balance	(27,024)	(19,124)	(27,024)	(19,124)	(27,024)	(19,124)
Accumulated Net Unrealized Investment Gain (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	(307)	(2,593)	(2,942)	40,190	(3,478)	32,296
Other Comprehensive Income (Loss) before Reclassifications	2,229	(1,000)	4,202	(3,159)	4,121	7,369
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	111	115	773	519	1,390	(2,115)
Accumulated Other Comprehensive Income (Loss), ending balance	2,033	(3,478)	2,033	(3,478)	2,033	(3,478)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	(10,819)	(11,253)	(10,919)	(11,342)	(11,144)	(11,514)
Other Comprehensive Income (Loss) before Reclassifications	0	0	0	0	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	117	109	217	198	442	370
Accumulated Other Comprehensive Income (Loss), ending balance	(10,702)	(11,144)	(10,702)	(11,144)	(10,702)	(11,144)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	(37,127)	(32,321)	(38,784)	11,058	(33,746)	(4,133)
Other Comprehensive Income (Loss) before Reclassifications	2,229	(1,000)	4,202	(3,159)	(468)	15,320
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(795)	(425)	(1,111)	(617)	(1,479)	(3,905)
Accumulated Other Comprehensive Income (Loss), ending balance	$ (35,693)	$ (33,746)	$ (35,693)	$ (33,746)	$ (35,693)	$ (33,746)