Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net Income	$ 16,778	$ 15,675	$ 36,363	$ 30,195
Unrealized Gain on Available-for-Sale Securities:
Reversal of Previously Recognized Gains Realized on Sale of Investments and Included in Other Income During Period	(1)		(1)
Gains Arising During Period	21	27	38	100
Income Tax Expense	(7)	(9)	(13)	(35)
Change in Unrealized Gains on Available-for-Sale Securities – net-of-tax	13	18	24	65
Pension and Postretirement Benefit Plans:
Amortization of Unrecognized Postretirement Benefit Losses and Costs (note 11)	159	155	316	309
Income Tax Expense	(63)	(63)	(126)	(124)
Pension and Postretirement Benefit Plans – net-of-tax	96	92	190	185
Total Other Comprehensive Income	109	110	214	250
Total Comprehensive Income	$ 16,887	$ 15,785	$ 36,577	$ 30,445