Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Pre-Tax Amount
Other Comprehensive Income/(Loss), Pre-Tax Amount	$ (10,055)	$ 22,033
Tax (Expense) Benefit
Other Comprehensive Income/(Loss), Tax (Expense) Benefit	2,145	(4,691)
Net of Tax Amount
Other Comprehensive Income/(Loss), Net of Tax Amount	(7,910)	17,342
Pension settlement charge	700
Accumulated Net Investment Gain (Loss) Attributable to Parent
Pre-Tax Amount
Change in net unrealized gains/(losses) on debt securities available-for-sale	(9,712)	21,568
Tax (Expense) Benefit
Change in net unrealized gains/(losses) on debt securities available-for-sale	2,072	(4,592)
Net of Tax Amount
Change in net unrealized gains/(losses) on debt securities available-for-sale	(7,640)	16,976
Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent
Pre-Tax Amount
Other Comprehensive Income/(Loss), Pre-Tax Amount	(343)	465
Tax (Expense) Benefit
Other Comprehensive Income/(Loss), Tax (Expense) Benefit	73	(99)
Net of Tax Amount
Other Comprehensive Income/(Loss), Net of Tax Amount	$ (270)	$ 366