Employee Benefit Plans (Fair Value Of Pension Plan Assets By Asset Category) (Details) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
U.S. government obligations		$ 917,147	$ 920,904
Government-sponsored enterprise obligations		406,363	449,998
State and municipal obligations		1,611,366	1,778,214
Agency mortgage-backed securities		3,040,913	2,685,931
Non-agency mortgage-backed securities		905,793	1,055,639
Asset-backed securities		1,492,800	2,381,301
Pension Plans [Member]
U.S. government obligations		3,719	3,621
Government-sponsored enterprise obligations	[1]	1,282	1,215
State and municipal obligations		8,527	9,148
Agency mortgage-backed securities	[2]	7,896	4,073
Non-agency mortgage-backed securities		4,891	5,437
Asset-backed securities		3,833	5,275
Corporate bonds	[3]	37,457	34,037
Mutual funds	[4]	6,979	10,393
Common stocks	[4]	23,744	20,141
International developed markets	[4]	7,870	5,100
Emerging markets	[4]	2,062	1,097
Total		108,260	99,537
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
U.S. government obligations		917,147	920,904
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		3,719	3,621
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]	6,979	10,393
Common stocks	[4]	23,744	20,141
International developed markets	[4]	7,870	5,100
Emerging markets	[4]	2,062	1,097
Total		44,374	40,352
Significant Other Observable Inputs (Level 2) [Member]
U.S. government obligations		0	0
Government-sponsored enterprise obligations		406,363	449,998
State and municipal obligations		1,594,350	1,761,532
Agency mortgage-backed securities		3,040,913	2,685,931
Non-agency mortgage-backed securities		905,793	1,055,639
Asset-backed securities		1,492,800	2,381,301
Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
U.S. government obligations		0	0
Government-sponsored enterprise obligations	[1]	1,282	1,215
State and municipal obligations		8,527	9,148
Agency mortgage-backed securities	[2]	7,896	4,073
Non-agency mortgage-backed securities		4,891	5,437
Asset-backed securities		3,833	5,275
Corporate bonds	[3]	37,457	34,037
Mutual funds	[4]	0	0
Common stocks	[4]	0	0
International developed markets	[4]	0	0
Emerging markets	[4]	0	0
Total		63,886	59,185
Significant Unobservable Inputs (Level 3) [Member]
U.S. government obligations		0	0
Government-sponsored enterprise obligations		0	0
State and municipal obligations		17,016	16,682
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, consumer goods, healthcare, electronic technology and technology services industries.