Accumulated Other Comrehensive Loss (Components of AOCI) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Amounts reclassified from accumulated other comprehensive loss	$ 18,292	$ 23,667
Net current period other comprehensive income (loss)	108,464	(62,842)	$ 12,898
Unrealized gains (losses) on securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' equity	(38,505)	(60,696)
Net unrealized gains (losses) arising during period	49,776	22,461
Amounts reclassified from accumulated other comprehensive loss	(5,479)	(270)
Net current period other comprehensive income (loss)	44,297	22,191
Stockholders' equity	5,792	(38,505)	(60,696)
Unrealized losses on securities available for sale transferred from (to) held to maturity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' equity	(71,149)	0
Net unrealized gains (losses) arising during period	55,834	(84,321)
Amounts reclassified from accumulated other comprehensive loss	15,315	13,172
Net current period other comprehensive income (loss)	71,149	(71,149)
Stockholders' equity	0	(71,149)	0
Defined Benefit Pension Items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' equity	(125,533)	(111,649)
Net unrealized gains (losses) arising during period	(15,438)	(24,649)
Amounts reclassified from accumulated other comprehensive loss	8,456	10,765
Net current period other comprehensive income (loss)	(6,982)	(13,884)
Stockholders' equity	(132,515)	(125,533)	(111,649)
Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' equity	(235,187)	(172,345)
Net unrealized gains (losses) arising during period	90,172	(86,509)
Amounts reclassified from accumulated other comprehensive loss	18,292	23,667
Net current period other comprehensive income (loss)	108,464	(62,842)	12,898
Stockholders' equity	$ (126,723)	(235,187)	(172,345)
Pre-adoption \| Unrealized gains (losses) on securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' equity		(30,945)
Stockholders' equity			(30,945)
Pre-adoption \| Unrealized losses on securities available for sale transferred from (to) held to maturity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' equity		0
Stockholders' equity			0
Pre-adoption \| Defined Benefit Pension Items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' equity		(91,349)
Stockholders' equity			(91,349)
Pre-adoption \| Accumulated Other Comprehensive Loss
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Stockholders' equity		$ (122,294)
Stockholders' equity			(122,294)
Effect of adoption
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments			(50,051)
Effect of adoption \| Unrealized gains (losses) on securities available for sale
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments			(29,751)
Effect of adoption \| Unrealized losses on securities available for sale transferred from (to) held to maturity
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments			0
Effect of adoption \| Defined Benefit Pension Items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect adjustments			$ (20,300)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

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