Pension and Other Post-Retirement Benefit Plans (Fair Value of Plan Assets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 44,150	$ 40,316	$ 37,724
Real estate [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	17,181	14,557	12,214
Hedge funds and private equity [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	26,969	25,759	25,510
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	682,553	594,697	588,494
Pension Plans [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	165,236	140,102
Pension Plans [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	473,167	414,279
Pension Plans [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	44,150	40,316
Pension Plans [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	682,553	594,697
Pension Plans [Member] | Temporary cash investments [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	14
Pension Plans [Member] | Temporary cash investments [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Temporary cash investments [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Temporary cash investments [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	14
Pension Plans [Member] | Common trust funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Common trust funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	5,720	17,495
Pension Plans [Member] | Common trust funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Common trust funds [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	5,720	17,495
Pension Plans [Member] | Corporate stock [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	63,396	49,169
Pension Plans [Member] | Corporate stock [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	2,123	197
Pension Plans [Member] | Corporate stock [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Corporate stock [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	65,519	49,366
Pension Plans [Member] | Mutual funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	96,008	73,910
Pension Plans [Member] | Mutual funds [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	138,846	125,027
Pension Plans [Member] | Mutual funds [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Mutual funds [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	234,854	198,937
Pension Plans [Member] | Fixed income investments [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	5,832	17,009
Pension Plans [Member] | Fixed income investments [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	326,478	271,560
Pension Plans [Member] | Fixed income investments [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Fixed income investments [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	332,310	288,569
Pension Plans [Member] | Real estate [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Real estate [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Real estate [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	17,181	14,557
Pension Plans [Member] | Real estate [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	17,181	14,557
Pension Plans [Member] | Hedge funds and private equity [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Hedge funds and private equity [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	0	0
Pension Plans [Member] | Hedge funds and private equity [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	26,969	25,759
Pension Plans [Member] | Hedge funds and private equity [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	$ 26,969	$ 25,759