Accumulated Other Comprehensive Income (Changes in AOCI by Component) (Details) - USD ($) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2020		Jun. 30, 2019		Jun. 30, 2020		Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		$ 137,207		$ 3,046		$ 40,367		$ (35,305)
Other comprehensive income before reclassifications	[1]	45,471		44,262		143,144		83,969
Amounts reclassified from accumulated other comprehensive income (2)	[1]	(1,601)		(158)		(2,434)		(1,514)
Net current-period other comprehensive income	[1]	43,870		44,104		140,710		82,455
Ending balance		181,077		47,150		181,077		47,150
Unrealized Gains and Losses on Available-for-Sale Debt Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		112,543		352		33,038		(33,128)
Other comprehensive income before reclassifications	[1]	42,860		37,029		122,556		71,926
Amounts reclassified from accumulated other comprehensive income (2)		0	[2]	(219)	[1]	(191)	[1]	(1,636)	[1]
Net current-period other comprehensive income	[1]	42,860		36,810		122,365		70,290
Ending balance		155,403		37,162		155,403		37,162
Unrealized Gains and Losses on Pension Plan Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(3,894)		(2,116)		(3,974)		(2,177)
Other comprehensive income before reclassifications	[1]	0		0		0		0
Amounts reclassified from accumulated other comprehensive income (2)	[1]	79		61		159		122
Net current-period other comprehensive income	[1]	79		61		159		122
Ending balance		(3,815)		(2,055)		(3,815)		(2,055)
Unrealized gains and losses on cash flow hedge
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		28,558		4,810		11,303		0
Other comprehensive income before reclassifications		2,611	[1]	7,233	[1]	20,588	[2]	12,043	[1]
Amounts reclassified from accumulated other comprehensive income (2)	[2]	(1,680)		0		(2,402)		0
Net current-period other comprehensive income	[1]	931		7,233		18,186		12,043
Ending balance		$ 29,489		$ 12,043		$ 29,489		$ 12,043

[1] All amounts are net of tax. Amounts in parentheses indicate debits.

[2] See following table for details about these reclassifications.