Fair value of financial instruments (Details)
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9 Months Ended |
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Sep. 30, 2016
USD ($)
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Mar. 31, 2016
USD ($)
derivative_instrument
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Dec. 31, 2015
USD ($)
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| Fixed-Rate Debt | Unsecured notes issued in a private placement |
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| Debt Instrument [Line Items] |
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| Carrying value |
$ 85,700,000
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$ 92,900,000
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| Fair Value, Inputs, Level 3 | Fixed-Rate Debt | Unsecured notes issued in a private placement |
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| Debt Instrument [Line Items] |
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| Fair value |
88,800,000
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$ 95,700,000
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| Not Designated as Hedging Instrument | Foreign Exchange Contract |
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| Debt Instrument [Line Items] |
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| Notional value |
$ 51,900,000.0
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| Weighted average maturity (in months) |
1 month
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| Designated as Hedging Instrument | Cross currency swap |
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| Debt Instrument [Line Items] |
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| Notional value |
$ 9,500,000.0
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| Weighted average maturity (in months) |
8 months
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| Designated as Hedging Instrument | Cross currency swap | Fair Value, Inputs, Level 2 |
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| Debt Instrument [Line Items] |
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| Derivative asset |
$ 3,800,000
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| Designated as Hedging Instrument | Interest Rate Swap |
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| Debt Instrument [Line Items] |
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| Notional value |
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$ 40,000,000
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| Number of interest rate swaps | derivative_instrument |
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2
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| Fair value liability interest rate swap |
500,000
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| Prepaid Expenses and Other Current Assets | Designated as Hedging Instrument | Cross currency swap | Fair Value, Inputs, Level 2 |
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| Debt Instrument [Line Items] |
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| Derivative asset |
2,400,000
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| Other Assets | Designated as Hedging Instrument | Cross currency swap | Fair Value, Inputs, Level 2 |
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| Debt Instrument [Line Items] |
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| Derivative asset |
$ 1,400,000
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