Employee Benefit Plans (Fair Value Of Pension Plan Assets By Asset Category) (Details) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
U.S. government obligations		$ 907,652	$ 917,147
Government-sponsored enterprise obligations		195,778	406,363
State and municipal obligations		1,328,039	1,611,366
Agency mortgage-backed securities		3,214,985	3,040,913
Non-agency mortgage-backed securities		1,047,716	905,793
Asset-backed securities		1,511,614	1,492,800
Pension Plans [Member]
U.S. government obligations		2,994	3,719
Government-sponsored enterprise obligations	[1]	1,200	1,282
State and municipal obligations		8,299	8,527
Agency mortgage-backed securities	[2]	8,209	7,896
Non-agency mortgage-backed securities		4,398	4,891
Asset-backed securities		3,520	3,833
Corporate bonds	[3]	37,207	37,457
Mutual funds	[4]	8,645	6,979
Common stocks	[4]	18,173	23,744
International developed markets	[4]	5,046	7,870
Emerging markets	[4]	1,727	2,062
Total		99,418	108,260
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
U.S. government obligations		907,652	917,147
Government-sponsored enterprise obligations		0	0
State and municipal obligations		0	0
Agency mortgage-backed securities		0	0
Non-agency mortgage-backed securities		0	0
Asset-backed securities		0	0
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] | Pension Plans [Member]
U.S. government obligations		2,994	3,719
Government-sponsored enterprise obligations	[1]	0	0
State and municipal obligations		0	0
Agency mortgage-backed securities	[2]	0	0
Non-agency mortgage-backed securities		0	0
Asset-backed securities		0	0
Corporate bonds	[3]	0	0
Mutual funds	[4]	8,645	6,979
Common stocks	[4]	18,173	23,744
International developed markets	[4]	5,046	7,870
Emerging markets	[4]	1,727	2,062
Total		36,585	44,374
Significant Other Observable Inputs (Level 2) [Member]
U.S. government obligations		0	0
Government-sponsored enterprise obligations		195,778	406,363
State and municipal obligations		1,313,881	1,594,350
Agency mortgage-backed securities		3,214,985	3,040,913
Non-agency mortgage-backed securities		1,047,716	905,793
Asset-backed securities		1,511,614	1,492,800
Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
U.S. government obligations		0	0
Government-sponsored enterprise obligations	[1]	1,200	1,282
State and municipal obligations		8,299	8,527
Agency mortgage-backed securities	[2]	8,209	7,896
Non-agency mortgage-backed securities		4,398	4,891
Asset-backed securities		3,520	3,833
Corporate bonds	[3]	37,207	37,457
Mutual funds	[4]	0	0
Common stocks	[4]	0	0
International developed markets	[4]	0	0
Emerging markets	[4]	0	0
Total		62,833	63,886
Significant Unobservable Inputs (Level 3) [Member]
U.S. government obligations		0	0
Government-sponsored enterprise obligations		0	0
State and municipal obligations		14,158	17,016
Agency mortgage-backed securities		0	0
Non-agency mortgage-backed securities		0	0
Asset-backed securities		0	0
Significant Unobservable Inputs (Level 3) [Member] | Pension Plans [Member]
U.S. government obligations		0	0
Government-sponsored enterprise obligations	[1]	0	0
State and municipal obligations		0	0
Agency mortgage-backed securities	[2]	0	0
Non-agency mortgage-backed securities		0	0
Asset-backed securities		0	0
Corporate bonds	[3]	0	0
Mutual funds	[4]	0	0
Common stocks	[4]	0	0
International developed markets	[4]	0	0
Emerging markets	[4]	0	0
Total		$ 0	$ 0

[1] This category represents bonds (excluding mortgage-backed securities) issued by agencies such as the Federal Home Loan Bank, the Federal Home Loan Mortgage Corp and the Federal National Mortgage Association.

[2] This category represents mortgage-backed securities issued by the agencies mentioned in (a).

[3] This category represents investment grade bonds issued in the U.S., primarily by domestic issuers, representing diverse industries.

[4] This category represents investments in individual common stocks and equity funds. These holdings are diversified, largely across the financial services, technology services, healthcare, electronic technology, and consumer goods industries.