Employee Benefit Plans (Fair Value Of Pension Plan Assets By Asset Category) (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
U.S. government obligations		$ 920,904	$ 727,076
Government-sponsored enterprise obligations		449,998	793,023
State and municipal obligations		1,778,214	1,741,957
Agency mortgage-backed securities		2,685,931	2,618,281
Non-agency mortgage-backed securities		1,055,639	879,963
Asset-backed securities		2,381,301	2,644,381
Pension Plans [Member]
U.S. government obligations		3,621	2,540
Government-sponsored enterprise obligations	[1]	1,215	1,208
State and municipal obligations		9,148	10,478
Agency mortgage-backed securities	[2]	4,073	1,352
Non-agency mortgage-backed securities		5,437	5,740
Asset-backed securities		5,275	6,965
Corporate bonds	[3]	34,037	32,800
U.S. large-cap	[4]	12,885	15,746
U.S. mid-cap	[4]	10,875	12,960
U.S. small-cap	[4]	2,447	2,545
International developed markets	[4]	5,100	3,125
Emerging markets	[4]	1,097	392
Money market funds	[4]	4,327	3,474
Total		99,537	99,325
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
U.S. government obligations		920,904	727,076
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		3,621	2,540
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
U.S. large-cap	[4]	12,885	15,746
U.S. mid-cap	[4]	10,875	12,960
U.S. small-cap	[4]	2,447	2,545
International developed markets	[4]	5,100	3,125
Emerging markets	[4]	1,097	392
Money market funds	[4]	4,327	3,474
Total		40,352	40,782
Significant Other Observable Inputs (Level 2) [Member]
U.S. government obligations		0	0
Government-sponsored enterprise obligations		449,998	793,023
State and municipal obligations		1,761,532	1,724,762
Agency mortgage-backed securities		2,685,931	2,618,281
Non-agency mortgage-backed securities		1,055,639	879,963
Asset-backed securities		2,381,301	2,644,381
Significant Other Observable Inputs (Level 2) [Member] | Pension Plans [Member]
U.S. government obligations		0	0
Government-sponsored enterprise obligations	[1]	1,215	1,208
State and municipal obligations		9,148	10,478
Agency mortgage-backed securities	[2]	4,073	1,352
Non-agency mortgage-backed securities		5,437	5,740
Asset-backed securities		5,275	6,965
Corporate bonds	[3]	34,037	32,800
U.S. large-cap	[4]	0	0
U.S. mid-cap	[4]	0	0
U.S. small-cap	[4]	0	0
International developed markets	[4]	0	0
Emerging markets	[4]	0	0
Money market funds	[4]	0	0
Total		59,185	58,543
Significant Unobservable Inputs (Level 3) [Member]
U.S. government obligations		0	0
Government-sponsored enterprise obligations		0	0
State and municipal obligations		16,682	17,195
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
U.S. large-cap	[4]	0	0
U.S. mid-cap	[4]	0	0
U.S. small-cap	[4]	0	0
International developed markets	[4]	0	0
Emerging markets	[4]	0	0
Money market funds	[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.