Pension and Postretirement Benefits - Fair value of the plans' assets by asset class (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Pension Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	$ 11,198	$ 10,872
Pension Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	10,941	10,655
Pension Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	257	217
Pension Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	0	0
US Postretirement Benefit Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		520
US Postretirement Benefit Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		520
US Postretirement Benefit Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		0
US Postretirement Benefit Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		0
Foreign Pension Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	11,747	11,560
Foreign Pension Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	11,327	11,165
Foreign Pension Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	420	395
Foreign Pension Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	0
Aggregate fixed income securities | Pension Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	6,534	5,966
Aggregate fixed income securities | Pension Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	6,534	5,966
Aggregate fixed income securities | Pension Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	0	0
Aggregate fixed income securities | Pension Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	0	0
Aggregate fixed income securities | US Postretirement Benefit Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		407
Aggregate fixed income securities | US Postretirement Benefit Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		407
Aggregate fixed income securities | US Postretirement Benefit Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		0
Aggregate fixed income securities | US Postretirement Benefit Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		0
U.S. equity securities | Pension Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	3,855	4,542
U.S. equity securities | Pension Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	3,855	4,542
U.S. equity securities | Pension Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	0	0
U.S. equity securities | Pension Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	0	0
U.S. equity securities | US Postretirement Benefit Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		109
U.S. equity securities | US Postretirement Benefit Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		109
U.S. equity securities | US Postretirement Benefit Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		0
U.S. equity securities | US Postretirement Benefit Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		0
U.S. equity securities | Foreign Pension Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	1,236	1,269
U.S. equity securities | Foreign Pension Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	1,236	1,269
U.S. equity securities | Foreign Pension Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		0
U.S. equity securities | Foreign Pension Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	0
Cash | Pension Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	552	147
Cash | Pension Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	552	147
Cash | Pension Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	0	0
Cash | Pension Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	0	0
Cash | US Postretirement Benefit Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		4
Cash | US Postretirement Benefit Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		4
Cash | US Postretirement Benefit Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		0
Cash | US Postretirement Benefit Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		0
Equity Securities | Pension Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	257	217
Equity Securities | Pension Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	0	0
Equity Securities | Pension Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	257	217
Equity Securities | Pension Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	0	0
Equity Securities | Foreign Pension Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	451	336
Equity Securities | Foreign Pension Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	451	336
Equity Securities | Foreign Pension Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		0
Equity Securities | Foreign Pension Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	0
Canadian Fixed Income Securities | Foreign Pension Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	5,367	5,174
Canadian Fixed Income Securities | Foreign Pension Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	5,367	5,174
Canadian Fixed Income Securities | Foreign Pension Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans		0
Canadian Fixed Income Securities | Foreign Pension Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	0
International equity securities | Foreign Pension Plans
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	4,693	4,781
International equity securities | Foreign Pension Plans | Quoted Prices in Active Markets (Level 1)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	4,273	4,386
International equity securities | Foreign Pension Plans | Significant Other Observable Inputs (Level 2)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	420	395
International equity securities | Foreign Pension Plans | Significant Unobserved Inputs (Level 3)
Fair value of the domestic plans assets by asset class
Fair value measurement domestic pension plans	$ 0