Risk Management and Use of Derivative Financial Instruments (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net
Derivatives not in cash flow hedging relationships, gain (loss), net	$ 1,020	$ 3,362	$ (857)
Embedded derivatives | Other income and expense
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net
Derivatives not in cash flow hedging relationships, gain (loss), net	1,378	1,159	(1,141)
Foreign currency forward | Other income and expense
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net
Derivatives not in cash flow hedging relationships, gain (loss), net	364	1,266	254
Put option | Other income and expense
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net
Derivatives not in cash flow hedging relationships, gain (loss), net	0	0	(2)
Stock warrants | Other income and expense
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net
Derivatives not in cash flow hedging relationships, gain (loss), net	66	297	66
Swaption | Other income and expense
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net
Derivatives not in cash flow hedging relationships, gain (loss), net	(700)	428	0
Interest rate swap | Interest Expense
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net
Derivatives not in cash flow hedging relationships, gain (loss), net	$ (88)	$ 212	$ (34)