Employee Benefit Plans - Net Periodic Benefit Cost (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 3,923		$ 8,452		$ 8,407
Interest cost	10,707		16,682		17,284
Expected return on plan assets	(15,258)		(25,302)		(25,477)
Amortization of prior service cost	576		1,296		1,308
Amortization of losses	6,542		20,097		17,578
Amortization of negative plan amendment	0		0		0
Curtailment expense	0		60		0
Settlement expense	0		817		0
Net periodic benefit cost	6,490	[1]	22,102	[1]	19,100	[1]
Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	402		1,056		918
Interest cost	537		937		956
Expected return on plan assets	0		0		0
Amortization of prior service cost	8		66		80
Amortization of losses	288		675		582
Amortization of negative plan amendment	(137)		(105)		(55)
Curtailment expense	0		0		0
Settlement expense	0		0		0
Net periodic benefit cost	1,098	[1]	2,629	[1]	2,481	[1]
Income (Loss) from Discontinued Operations, Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 4,000		$ 14,900		$ 12,800

[1] Net periodic benefit cost for the years ended December 31, 2014, 2013 and 2012 included $4.0 million, $14.9 million, and $12.8 million, respectively, recorded in “Income from discontinued operations, net” on the Consolidated Statements of Income and Comprehensive Income.