Risk Management and Use of Derivative Financial Instruments (Details 6) In Thousands, unless otherwise specified		3 Months Ended
	Mar. 31, 2013 USD ($)	Mar. 31, 2013 Designated as Hedging Foreign currency collars USD ($)	Mar. 31, 2013 Designated as Hedging Foreign currency collars EUR (€)	Mar. 31, 2013 Designated as Hedging Foreign currency collars Minimum	Mar. 31, 2013 Designated as Hedging Foreign currency collars Maximum	Mar. 31, 2013 Designated as Hedging Foreign exchange forward January USD ($)	Mar. 31, 2013 Designated as Hedging Foreign exchange forward January EUR (€)	Mar. 31, 2013 Designated as Hedging Foreign exchange forward January Minimum	Mar. 31, 2013 Designated as Hedging Foreign exchange forward January Maximum	Mar. 31, 2013 Designated as Hedging Foreign exchange forward May USD ($)	Mar. 31, 2013 Designated as Hedging Foreign exchange forward May EUR (€)	Mar. 31, 2013 Designated as Hedging Foreign exchange forward May Minimum	Mar. 31, 2013 Designated as Hedging Foreign exchange forward May Maximum	Mar. 31, 2013 Designated as Hedging Foreign exchange forward July USD ($)	Mar. 31, 2013 Designated as Hedging Foreign exchange forward July EUR (€)	Mar. 31, 2013 Designated as Hedging Foreign exchange forward September USD ($)	Mar. 31, 2013 Designated as Hedging Foreign exchange forward September EUR (€)	Mar. 31, 2013 Designated as Hedging Foreign exchange forward September Minimum	Mar. 31, 2013 Designated as Hedging Foreign exchange forward September Maximum	Mar. 31, 2013 Designated as Hedging Foreign exchange forward December USD ($)	Mar. 31, 2013 Designated as Hedging Foreign exchange forward December EUR (€)	Mar. 31, 2013 Designated as Hedging Foreign exchange forward December Minimum	Mar. 31, 2013 Designated as Hedging Foreign exchange forward December Maximum	Mar. 31, 2013 Designated as Hedging Foreign exchange forward December Yen USD ($)	Mar. 31, 2013 Designated as Hedging Foreign exchange forward December Yen JPY (¥)	Mar. 31, 2013 Designated as Hedging Foreign exchange forward December Yen Minimum	Mar. 31, 2013 Designated as Hedging Foreign exchange forward December Yen Maximum	Mar. 31, 2013 Not Designated Foreign exchange forward December Yen USD ($)	Mar. 31, 2013 Not Designated Foreign exchange forward December Yen JPY (¥)
Derivative Instrument Detail
Notional amount, foreign currency derivatives			€ 30,365				€ 11,342				€ 56,700				€ 45,000		€ 24,628				€ 17,100				¥ 1,002,834				¥ 610,129
Derivative, Floor Price		1.40	1.40			1.34	1.34			1.28	1.28			1.39	1.39	1.34	1.34			1.34	1.34			0.0122	0.0122			0.0128	0.0128
Derivative, Cap Price		1.42	1.42							1.29	1.29					1.35	1.35							0.0128	0.0128
Effective Date		Sep. 01, 2011	Sep. 01, 2011			Jan. 01, 2013	Jan. 01, 2013			May 01, 2012	May 01, 2012			Jul. 01, 2011	Jul. 01, 2011	Sep. 01, 2011	Sep. 01, 2011			Dec. 01, 2012	Dec. 01, 2012			Dec. 01, 2012	Dec. 01, 2012			Dec. 01, 2012	Dec. 01, 2012
Expiration Date				Jun. 01, 2013	Sep. 01, 2014			Sep. 01, 2015	Mar. 01, 2016			Dec. 01, 2014	Jun. 01, 2017	Jul. 01, 2013	Jul. 01, 2013			Sep. 01, 2017	Mar. 01, 2015			Sep. 01, 2017	Mar. 01, 2018			Jun. 01, 2013	Dec. 01, 2017	Dec. 01, 2017	Dec. 01, 2017
Fair value, foreign currency derivatives	$ 12,869	$ 3,542				$ 544				$ (198)				$ 4,745		$ 1,405				$ 525				$ 1,488				$ 818