Hedges and Other Derivative Financial Instruments (Details) (Free standing derivatives [Member]) In Thousands, unless otherwise specified	6 Months Ended				6 Months Ended				6 Months Ended				6 Months Ended
	Jun. 30, 2012 USD ($)	Jun. 30, 2011 USD ($)	Jun. 30, 2012 Pound Sterling [Member] USD ($)	Jun. 30, 2012 Pound Sterling [Member] GBP (£)	Jun. 30, 2012 Euro [Member] USD ($)	Jun. 30, 2011 Euro [Member] USD ($)	Jun. 30, 2012 Euro [Member] EUR (€)	Jun. 30, 2011 Euro [Member] EUR (€)	Jun. 30, 2012 Japanese Yen [Member] USD ($)	Jun. 30, 2011 Japanese Yen [Member] USD ($)	Jun. 30, 2012 Japanese Yen [Member] JPY (¥)	Jun. 30, 2011 Japanese Yen [Member] JPY (¥)	Jun. 30, 2012 Maximum [Member] Pound Sterling [Member]	Jun. 30, 2012 Maximum [Member] Euro [Member]	Jun. 30, 2012 Maximum [Member] Japanese Yen [Member]	Jun. 30, 2012 Minimum [Member] Pound Sterling [Member]	Jun. 30, 2012 Minimum [Member] Euro [Member]	Jun. 30, 2012 Minimum [Member] Japanese Yen [Member]
Summary of net forward currency sell contracts under freestanding derivatives
Contract amount	$ 112,532	$ 38,793	$ 29,474	£ 18,765	$ 64,999	$ 22,720	€ 49,000	€ 16,000	$ 18,059	$ 16,073	¥ 1,430,000	¥ 1,250,000
Market value	108,537	36,974	28,569		62,032	20,733			17,936	16,241
Net unrealized appreciation (depreciation)	$ 3,995	$ 1,819	$ 905		$ 2,967	$ 1,987			$ 123	$ (168)
Expiration date					Jan. 31, 2012				Feb. 29, 2012				Apr. 05, 2013	Apr. 30, 2013	Nov. 21, 2001	Jul. 06, 2012	Jul. 31, 2012	Aug. 23, 2012