Fair value - pensions (Details 9) (Pension Benefits, USD $)	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	$ 309,184,000		$ 278,000,000		$ 277,598,000
Percentage investment in common stock of mid-cap U.S. companies	12.00%		26.00%
Percentage investment in common stock of large-cap U.S. companies	26.00%		26.00%
Percentage investment in US Treasuries	13.00%		13.00%
Percentage investment in corporate bonds	41.00%		6.00%
Percentage investment in other investments	8.00%		29.00%
Estimated future employer contributions in next fiscal year	18,100,000
Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	12,605,000		19,790,000
Equity securities of U.S. companies
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	86,981,000		99,315,000
Equities Securities of International companies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	39,818,000		35,353,000
Collective and Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	102,852,000	[1]	58,755,000	[2]
Corporate debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	45,112,000		23,868,000
Mortgage-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year			22,987,000
Municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	9,302,000		9,290,000
U.S. Treasury securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	12,514,000		8,642,000
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	219,711,000		180,138,000
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	2,145,000		2,256,000
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities of U.S. companies
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	86,981,000		99,315,000
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equities Securities of International companies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	39,818,000		35,353,000
Quoted Prices in Active Markets for Identical Assets (Level 1) | Collective and Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	82,787,000	[1]	43,214,000	[2]
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year			0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	0		0
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	7,980,000		0
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	89,473,000		97,573,000
Significant Other Observable Inputs (Level 2) | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	10,460,000		17,534,000
Significant Other Observable Inputs (Level 2) | Equity securities of U.S. companies
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	0		0
Significant Other Observable Inputs (Level 2) | Equities Securities of International companies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	0		0
Significant Other Observable Inputs (Level 2) | Collective and Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	20,065,000	[1]	15,541,000	[2]
Significant Other Observable Inputs (Level 2) | Corporate debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	45,112,000		23,579,000
Significant Other Observable Inputs (Level 2) | Mortgage-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year			22,987,000
Significant Other Observable Inputs (Level 2) | Municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	9,302,000		9,290,000
Significant Other Observable Inputs (Level 2) | U.S. Treasury securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	4,534,000		8,642,000
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	0		289,000
Significant Unobservable Inputs (Level 3) | Cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	0		0
Significant Unobservable Inputs (Level 3) | Equity securities of U.S. companies
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	0		0
Significant Unobservable Inputs (Level 3) | Equities Securities of International companies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	0		0
Significant Unobservable Inputs (Level 3) | Collective and Mutual funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	0	[1]	0	[2]
Significant Unobservable Inputs (Level 3) | Corporate debt securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	0		289,000
Significant Unobservable Inputs (Level 3) | Mortgage-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year			0
Significant Unobservable Inputs (Level 3) | Municipal bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	0		0
Significant Unobservable Inputs (Level 3) | U.S. Treasury securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of net plan assets at end of year	$ 0		$ 0

[1] Collective and mutual funds invest approximately 12 percent in common stock of mid-cap U.S. companies, 26 percent in common stock of large-cap U.S. companies, 13 percent in U.S. Treasuries, 41 percent in corporate bonds and 8 percent in other investments.

[2] Collective and mutual funds invest approximately 26 percent in common stock of mid-cap U.S. companies, 26 percent in common stock of large-cap U.S. companies, 13 percent in U.S. Treasuries, 6 percent in corporate bonds and 29 percent in other investments.