Benefit Plans and Other Postretirement Benefits, Changes in Level 3 Postretirement Benefit Plan Assets (Details) (Postretirement Benefit Plan [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Dec. 31	$ 46,222	$ 39,679	$ 39,946
Level 3 [Member]
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	3,265	2,065	5,018
Net realized gains (losses)	(102)	(159)	(113)
Net unrealized gains (losses)	556	93	407
Purchases, issuances and settlements, net	195	1,266	(3,247)
Fair value of plan assets at Dec. 31	3,914	3,265	2,065
Asset-backed Securities [Member]
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Dec. 31	73	730
Asset-backed Securities [Member] | Level 3 [Member]
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	730	245	752
Net realized gains (losses)	(32)	(2)	(25)
Net unrealized gains (losses)	179	(101)	75
Purchases, issuances and settlements, net	(804)	588	(557)
Fair value of plan assets at Dec. 31	73	730	245
Mortgage-backed Securities [Member]
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Dec. 31	3,841	2,535
Mortgage-backed Securities [Member] | Level 3 [Member]
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1	2,535	1,820	4,266
Net realized gains (losses)	(70)	(157)	(88)
Net unrealized gains (losses)	377	194	332
Purchases, issuances and settlements, net	999	678	(2,690)
Fair value of plan assets at Dec. 31	$ 3,841	$ 2,535	$ 1,820