Financial Results by Quarter Financial Results by Quarter (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 470,159	$ 487,845	$ 471,002	$ 460,824	$ 462,701	$ 480,233	$ 473,572	$ 457,798	$ 1,889,830	$ 1,874,304	$ 1,927,973
Costs and expenses:
Cost of sales	(401,404)	(441,237)	(414,521)	(414,209)	(396,428)	(409,822)	(398,546)	(403,076)	(1,671,371)	(1,607,872)	(1,702,530)
Selling, general and administrative expenses	(30,466)	(27,766)	(26,767)	(34,132)	(30,793)	(30,649)	(30,529)	(29,074)	(119,131)	(121,045)	(109,998)
Total operating costs and expenses	(431,870)	(469,003)	(441,288)	(448,341)	(427,221)	(440,471)	(429,075)	(432,150)	(1,790,502)	(1,728,917)	(1,812,528)
Income from operations	38,289	18,842	29,714	12,483	35,480	39,762	44,497	25,648	99,328	145,387	115,445
Net earnings	$ 82,862	$ 13,317	$ 11,658	$ (882)	$ 19,852	$ 19,064	$ 21,489	$ 3,726	$ 106,955	$ 64,131	$ 39,674
Net earnings per common share:
Basic (in dollars per share)	$ 3.91	$ 0.60	$ 0.52	$ (0.04)	$ 0.86	$ 0.82	$ 0.92	$ 0.16	$ 4.84	$ 2.75	$ 1.73
Diluted (in dollars per share)	$ 3.87	$ 0.60	$ 0.52	$ (0.04)	$ 0.84	$ 0.80	$ 0.91	$ 0.16	$ 4.80	$ 2.72	$ 1.66