Benefit Plans and Other Postretirement Benefits, Changes in Level 3 Postretirement Benefit Plan Assets (Details) - Postretirement Benefit Plan - 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		$ 45,356	$ 46,738
Fair value of plan assets at Dec. 31		42,684	45,356	$ 46,738
Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		0	0	3,914
Net realized gains (losses)				0
Net unrealized gains (losses)				0
Purchases, issuances and settlements, net				0
Transfers in (out) of Level 3	[1]			(3,914)
Fair value of plan assets at Dec. 31		0	0	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		2,736	345
Asset-backed securities | Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		0	0	73
Net realized gains (losses)				0
Net unrealized gains (losses)				0
Purchases, issuances and settlements, net				0
Transfers in (out) of Level 3	[1]			(73)
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		1,074
Fair value of plan assets at Dec. 31		3,396	1,074
Mortgage-backed securities | Level 3
Changes in Level 3 Plan Assets [Roll Forward]
Fair value of plan assets at Jan. 1		0	0	3,841
Net realized gains (losses)				0
Net unrealized gains (losses)				0
Purchases, issuances and settlements, net				0
Transfers in (out) of Level 3	[1]			(3,841)
Fair value of plan assets at Dec. 31		$ 0	$ 0	$ 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.