Other Comprehensive Income (Components of OCI) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Unrealized gains and losses on available for sale debt securities:
Net unrealized gains arising during the period	$ 22,563	$ 10,417
Reclassification adjustment for gains included in net income	0	0
Total	22,563	10,417
Unrealized losses on derivatives (cash flow hedges)	(7,697)	(432)
Amortization related to post-retirement obligations	112	(16)
Total other comprehensive income	14,978	9,969
Unrealized gains on available for sale debt securities:
Net unrealized gains arising during the period	(5,817)	(2,839)
Reclassification adjustment for gains included in net income	0	0
Total	(5,817)	(2,839)
Unrealized losses on derivatives (cash flow hedges)	1,984	118
Amortization related to post-retirement obligations	(28)	4
Total other comprehensive income	(3,861)	(2,717)
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent [Abstract]
Net unrealized gains arising during the period	16,746	7,578
Reclassification adjustment for gains included in net income	0	0
Total	16,746	7,578
Unrealized losses on derivatives (cash flow hedges)	(5,713)	(314)
Amortization related to post-retirement obligations	84	(12)
Total other comprehensive income	$ 11,117	$ 7,252