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, 2014
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1				$ 45,356
Fair value of plan assets at Dec. 31	46,738		46,222	45,356
Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	3,914		3,265	0
Net realized gains (losses)	0		(102)
Net unrealized gains (losses)	0		556
Purchases, issuances and settlements, net	0		195
Transfers in (out) of Level 3	(3,914)	[1]	0
Fair value of plan assets at Dec. 31	0		3,914	0
Asset-backed securities
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1				345
Fair value of plan assets at Dec. 31	319			345
Asset-backed securities | Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	73		730	0
Net realized gains (losses)	0		(32)
Net unrealized gains (losses)	0		179
Purchases, issuances and settlements, net	0		(804)
Transfers in (out) of Level 3	(73)	[1]	0
Fair value of plan assets at Dec. 31	0		73	0
Mortgage-backed securities
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1				1,074
Fair value of plan assets at Dec. 31	2,303			1,074
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	0
Net realized gains (losses)	0		(70)
Net unrealized gains (losses)	0		377
Purchases, issuances and settlements, net	0		999
Transfers in (out) of Level 3	(3,841)	[1]	0
Fair value of plan assets at Dec. 31	$ 0		$ 3,841	$ 0

[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.