Derivative instruments (Amount and balance sheet location) (Details) $ in Thousands		Jun. 30, 2016 USD ($) derivatives	Dec. 31, 2015 USD ($)
Not designated as hedging instruments | Foreign exchange contracts
Summary of amount of derivatives designated as hedging instruments
Net Notional Exposure		$ 297,275	$ 255,840
Not designated as hedging instruments | Foreign exchange contracts | Other assets
Summary of amount of derivatives designated as hedging instruments
Fair value, derivative assets	[1]	4,230	2,601
Not designated as hedging instruments | Foreign exchange contracts | Accounts payable and accrued expenses
Summary of amount of derivatives designated as hedging instruments
Fair value, derivative liabilities	[1]	4,746	3,211
Designated as hedging instruments | Interest rate swap contracts
Summary of amount of derivatives designated as hedging instruments
Net Notional Exposure		552,263	552,263
Designated as hedging instruments | Interest rate swap contracts | Other assets
Summary of amount of derivatives designated as hedging instruments
Fair value, derivative assets	[2]	20	21
Designated as hedging instruments | Interest rate swap contracts | Accounts payable and accrued expenses
Summary of amount of derivatives designated as hedging instruments
Fair value, derivative liabilities	[2]	$ 2,529	$ 1,942
Junior Subordinated Deferrable Debentures | Interest rate swap contracts
Summary of amount of derivatives designated as hedging instruments
Derivative, number of instruments held | derivatives		2
Flagstone Junior Subordinated Deferrable Debentures | Interest rate swap contracts
Summary of amount of derivatives designated as hedging instruments
Derivative, number of instruments held | derivatives		3
Flagstone Junior Subordinated Deferrable Debentures | Cross-currency interest rate swap
Summary of amount of derivatives designated as hedging instruments
Derivative, number of instruments held | derivatives		1

[1] Asset and liability derivatives are classified within other assets and accounts payable and accrued expenses, respectively, on the Consolidated Balance Sheets. The net impact on earnings, recognized in income within foreign exchange gains (losses) relating to the foreign currency forward contracts that were not designated as hedging instruments during the three and six months ended June 30, 2016 was $896 and ($1,117), respectively (2015: $nil and $nil, respectively). The net impact on earnings, recognized in income within other income (loss) relating to the foreign currency forward contracts that were not designated as hedging instruments during the three and six months ended June 30, 2016 were $84 and $120, respectively (2015: ($128) and ($127), respectively).

[2] Asset and liability derivatives are classified within other assets and accounts payable and accrued expenses, respectively, on the Consolidated Balance Sheets.