Accumulated Other Comprehensive Income (Changes in AOCI by Component) (Details) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2019		Sep. 30, 2018		Sep. 30, 2019		Sep. 30, 2018		Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		$ 47,150		$ (55,921)		$ (35,305)		$ (22,225)
Other comprehensive income before reclassifications	[1]	17,730		(14,149)		101,699		(48,043)
Amounts reclassified from accumulated other comprehensive income (2)	[1]	4		61		(1,510)		102
Net current-period other comprehensive income	[1]	17,734		(14,088)		100,189		(47,941)
Ending balance		64,884		(70,009)		64,884		(70,009)
Unrealized Gains and Losses on Available-for-Sale Debt Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		37,162		(53,597)		(33,128)		(19,779)
Other comprehensive income before reclassifications	[1]	14,593		(14,149)		86,519		(48,043)
Amounts reclassified from accumulated other comprehensive income (2)		0	[2]	0	[1]	(1,636)	[1]	(81)	[1]
Net current-period other comprehensive income	[1]	14,593		(14,149)		84,883		(48,124)
Ending balance		51,755		(67,746)		51,755		(67,746)
Unrealized Gains and Losses on Pension Plan Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(2,055)		(2,324)		(2,177)		(2,446)
Other comprehensive income before reclassifications	[1]	0		0		0		0
Amounts reclassified from accumulated other comprehensive income (2)	[1]	62		61		184		183
Net current-period other comprehensive income	[1]	62		61		184		183
Ending balance		(1,993)		(2,263)		(1,993)		(2,263)
Unrealized gains and losses on cash flow hedge
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		12,043		0		0		0
Other comprehensive income before reclassifications		3,137	[1]	0	[1]	15,180	[2]	0	[1]
Amounts reclassified from accumulated other comprehensive income (2)	[2]	(58)		0		(58)		0
Net current-period other comprehensive income	[1]	3,079		0		15,122		0
Ending balance		$ 15,122		$ 0		$ 15,122		$ 0
Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption										$ 0
Accounting Standards Update 2016-01 [Member] | Unrealized Gains and Losses on Available-for-Sale Debt Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption										157
Accounting Standards Update 2016-01 [Member] | Unrealized Gains and Losses on Pension Plan Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption										0
Accounting Standards Update 2016-01 [Member] | Unrealized gains and losses on cash flow hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption										0
Accounting Standards Update 2016-01 [Member] | Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption										$ 157

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

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