Benefit Plans and Other Postretirement Benefits, Changes in Level 3 Pension Plan Assets (Details) - Pension Plans - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		$ 1,103,865	$ 1,067,057
Fair value of plan assets at Dec. 31		1,036,681	1,103,865	$ 1,067,057
Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		68,620	64,578	82,991
Net realized gains (losses)		9,561	9,675	6,204
Net unrealized gains (losses)		(22,407)	(4,601)	(258)
Purchases, issuances and settlements, net		(2,740)	(1,032)	1,967
Transfers in (out) of Level 3		0	0	(26,326)	[1]
Fair value of plan assets at Dec. 31		53,034	68,620	64,578
Asset-backed securities
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		1,360
Fair value of plan assets at Dec. 31		881	1,360
Asset-backed securities | Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		0	0	4,604
Net realized gains (losses)				0
Net unrealized gains (losses)				0
Purchases, issuances and settlements, net				0
Transfers in (out) of Level 3	[1]			(4,604)
Fair value of plan assets at Dec. 31		0	0	0
Mortgage-backed securities
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		3,997
Fair value of plan assets at Dec. 31			3,997
Mortgage-backed securities | Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		0	0	12,058
Net realized gains (losses)				0
Net unrealized gains (losses)				0
Purchases, issuances and settlements, net				0
Transfers in (out) of Level 3	[1]			(12,058)
Fair value of plan assets at Dec. 31			0	0
Private equity investments
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		50,210
Fair value of plan assets at Dec. 31		34,353	50,210
Private equity investments | Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		50,210	49,022	47,056
Net realized gains (losses)		7,636	8,495	7,074
Net unrealized gains (losses)		(20,036)	(4,299)	(4,027)
Purchases, issuances and settlements, net		(3,457)	(3,008)	(1,081)
Transfers in (out) of Level 3		0	0	0	[1]
Fair value of plan assets at Dec. 31		34,353	50,210	49,022
Real estate
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		18,410	15,556
Fair value of plan assets at Dec. 31		18,681	18,410	15,556
Real estate | Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		18,410	15,556	19,273
Net realized gains (losses)		1,925	1,180	(870)
Net unrealized gains (losses)		(2,371)	(302)	3,769
Purchases, issuances and settlements, net		717	1,976	3,048
Transfers in (out) of Level 3		0	0	(9,664)	[1]
Fair value of plan assets at Dec. 31		$ 18,681	$ 18,410	$ 15,556

[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.