Accumulated Other Comprehensive Income (Changes in AOCI by Component) (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019		Mar. 31, 2018		Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		$ (35,305)		$ (22,225)
Other comprehensive income before reclassifications	[1]	36,873		(26,048)
Amounts reclassified from accumulated other comprehensive loss (2)	[1]	1,478		(17)
Net current-period other comprehensive income	[1]	38,351		(26,065)
Ending balance		3,046		(48,133)
Unrealized Gains and Losses on Available-for-Sale Debt Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(33,128)		(19,779)
Other comprehensive income before reclassifications	[1]	32,063		(26,048)
Amounts reclassified from accumulated other comprehensive loss (2)		1,417	[2]	(78)	[1]
Net current-period other comprehensive income	[1]	33,480		(26,126)
Ending balance		352		(45,748)
Unrealized Gains and Losses on Pension Plan Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(2,177)		(2,446)
Other comprehensive income before reclassifications	[1]	0		0
Amounts reclassified from accumulated other comprehensive loss (2)	[1]	61		61
Net current-period other comprehensive income	[1]	61		61
Ending balance		(2,116)		(2,385)
Unrealized gains and losses on cash flow hedge
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		0		0
Other comprehensive income before reclassifications	[1]	4,810		0
Amounts reclassified from accumulated other comprehensive loss (2)	[2]	0		0
Net current-period other comprehensive income	[1]	4,810		0
Ending balance		$ 4,810		$ 0
Accounting Standards Update 2016-01 [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption						$ (46)
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.