Comprehensive Income (Reclassification Out of AOCI) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income before income taxes	$ 163,437	$ 162,720	$ 228,952
Tax impact	(30,544)	(47,242)	(75,638)
Net income	132,893	115,478	153,314
Pension Benefits [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior-service costs	(45)	(8)
Actuarial gains/(losses)	19,951	36,930
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension Benefits [Member] | Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior-service costs	(45)	(8)	199
Actuarial gains/(losses)	(19,951)	(36,930)	(29,890)
Pension settlement costs		(44,163)
Income before income taxes	(19,996)	(81,101)	(29,691)
Tax impact	7,497	30,818	11,282
Net income	(12,499)	(50,283)	(18,409)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Postretirement Costs [Member] | Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior-service costs	3,911	6,101	10,068
Actuarial gains/(losses)	(2,916)	(7,846)	(7,537)
Income before income taxes	995	(1,745)	2,531
Tax impact	(373)	663	(962)
Net income	$ 622	$ (1,082)	$ 1,569