Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 112,633	$ 118,387	$ 93,949
Unrealized gains and losses on available for sale debt securities:
Net unrealized gains (losses) arising during the period	18,351	(6,129)	(2,163)
Reclassification adjustment for gains (losses) included in net income	0	0	0
Total	18,351	(6,129)	(2,163)
Unrealized (losses) gains on derivatives (cash flow hedges)	(579)	221	379
Amortization related to post-retirement obligations	(1,615)	1,221	(889)
Total other comprehensive income (loss)	16,157	(4,687)	(2,673)
Total comprehensive income	$ 128,790	$ 113,700	$ 91,276

Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.

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