Derivative instruments (Amount and balance sheet location) (Details) $ in Thousands		Dec. 31, 2015 USD ($) derivatives	Dec. 31, 2014 USD ($) derivatives
Not designated as hedging instruments
Summary of amount of derivatives designated as hedging instruments
Derivative, Number of Instruments Held | derivatives			1
Not designated as hedging instruments | Foreign currency forward contracts
Summary of amount of derivatives designated as hedging instruments
Notional amount		$ 255,840	$ 26,755
Not designated as hedging instruments | Foreign currency forward contracts | Other assets
Summary of amount of derivatives designated as hedging instruments
Fair value, derivative assets	[1]	2,601	1,685
Not designated as hedging instruments | Foreign currency forward contracts | Accounts payable and accrued expenses
Summary of amount of derivatives designated as hedging instruments
Fair value, derivative liabilities	[1]	3,211	0
Designated as hedging instruments | Foreign currency forward contracts
Summary of amount of derivatives designated as hedging instruments
Notional amount		0	210,333
Designated as hedging instruments | Foreign currency forward contracts | Other assets
Summary of amount of derivatives designated as hedging instruments
Fair value, derivative assets	[2]	0	408
Designated as hedging instruments | Foreign currency forward contracts | Accounts payable and accrued expenses
Summary of amount of derivatives designated as hedging instruments
Fair value, derivative liabilities	[2]	0	2,813
Designated as hedging instruments | Interest rate swap contracts
Summary of amount of derivatives designated as hedging instruments
Notional amount		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]	21	25
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]	$ 1,942	$ 1,169
Junior Subordinated Deferrable Debentures [Member] | 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 [Member] | 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 [Member] | 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) and other income (loss), relating to the foreign currency forward contracts that were not designated as hedging instruments during the year ended December 31, 2015 was $(610) and $139, respectively (2014: $nil and $(133), respectively).

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