Benefit Plans and Other Postretirement Benefits, Changes in Level 3 Postretirement Benefit Plan Assets (Details) (Postretirement Benefit Plan, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Dec. 31	$ 46,738		$ 46,222	$ 39,679
Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	3,914		3,265	2,065
Net realized gains (losses)	0		(102)	(159)
Net unrealized gains (losses)	0		556	93
Purchases, issuances and settlements, net	0		195	1,266
Transfers in (out) of Level 3	(3,914)	[1]	0
Fair value of plan assets at Dec. 31	0		3,914	3,265
Asset-backed securities
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Dec. 31	319		73
Asset-backed securities | Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	73		730	245
Net realized gains (losses)	0		(32)	(2)
Net unrealized gains (losses)	0		179	(101)
Purchases, issuances and settlements, net	0		(804)	588
Transfers in (out) of Level 3	(73)	[1]	0
Fair value of plan assets at Dec. 31	0		73	730
Mortgage-backed securities
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Dec. 31	2,303		3,841
Mortgage-backed securities | Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	3,841		2,535	1,820
Net realized gains (losses)	0		(70)	(157)
Net unrealized gains (losses)	0		377	194
Purchases, issuances and settlements, net	0		999	678
Transfers in (out) of Level 3	(3,841)	[1]	0
Fair value of plan assets at Dec. 31	$ 0		$ 3,841	$ 2,535

[1] Transfers out of Level 3 into Level 2 were principally due to diminished use of unobservable inputs that were previously significant to these fair value measurements and were subsequently sold during 2013.