Benefit Plans and Other Postretirement Benefits (Details 4) (Pension Benefits, USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure
Fair value of pension plan assets	$ 334,423	$ 295,054	$ 296,530
Equity securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	208,235	180,479
U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	93,047	80,651
U.S. equities - small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	25,159	22,579
International equities - growth
Defined Benefit Plan Disclosure
Fair value of pension plan assets	42,057	35,878
International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	47,972	41,371
Fixed income securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	123,315	111,490
U.S. fixed income securities - intermediate term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	59,983	54,398
U.S. fixed income securities - high yield
Defined Benefit Plan Disclosure
Fair value of pension plan assets	22,409	18,490
International fixed income securities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	40,923	38,602
Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of pension plan assets	2,873	3,085
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure
Fair value of pension plan assets	181,857	178,463
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	119,001	120,980
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	71,668	80,651
Quoted Prices in Active Markets for Identical Assets (Level 1) | International equities - growth
Defined Benefit Plan Disclosure
Fair value of pension plan assets	42,057	35,878
Quoted Prices in Active Markets for Identical Assets (Level 1) | International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	5,276	4,451
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed income securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	59,983	54,398
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. fixed income securities - intermediate term
Defined Benefit Plan Disclosure
Fair value of pension plan assets	59,983	54,398
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure
Fair value of pension plan assets	2,873	3,085
Significant Observable Inputs (Level 2)
Defined Benefit Plan Disclosure
Fair value of pension plan assets	152,566	116,591
Significant Observable Inputs (Level 2) | Equity securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	89,234	59,499
Significant Observable Inputs (Level 2) | U.S. equities - large cap
Defined Benefit Plan Disclosure
Fair value of pension plan assets	21,379
Significant Observable Inputs (Level 2) | U.S. equities - small/mid cap and other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	25,159	22,579
Significant Observable Inputs (Level 2) | International equities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	42,696	36,920
Significant Observable Inputs (Level 2) | Fixed income securities
Defined Benefit Plan Disclosure
Fair value of pension plan assets	63,332	57,092
Significant Observable Inputs (Level 2) | U.S. fixed income securities - high yield
Defined Benefit Plan Disclosure
Fair value of pension plan assets	22,409	18,490
Significant Observable Inputs (Level 2) | International fixed income securities - other
Defined Benefit Plan Disclosure
Fair value of pension plan assets	$ 40,923	$ 38,602