Derivative Instruments (Details) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended				3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2012 USD ($) Number	Jun. 30, 2011 USD ($)	Jun. 30, 2012 USD ($) Number	Jun. 30, 2011 USD ($)	Feb. 15, 2012 CAD	Dec. 31, 2011 USD ($)	Jun. 30, 2012 Interest Rate Swap [Member] USD ($)	Jun. 30, 2011 Interest Rate Swap [Member] USD ($)	Jun. 30, 2012 Interest Rate Swap [Member] USD ($)	Jun. 30, 2011 Interest Rate Swap [Member] USD ($)	Jun. 30, 2012 Foreign Exchange Contract [Member] USD ($)	Jun. 30, 2011 Foreign Exchange Contract [Member] USD ($)	Jun. 30, 2012 Foreign Exchange Contract [Member] USD ($)	Jun. 30, 2011 Foreign Exchange Contract [Member] USD ($)
Derivative Instruments (Textual) [Abstract]
Other liabilities	$ 400,065		$ 400,065			$ 371,557
Number of interest rate swaps	5		5
Foreign exchange contract					250,000
Gain (loss) on recognized in OCI							806	(4,962)	1,545	(7,016)	6,916	0	6,916	0
Gain (loss) reclassified from AOCI into income							360	(794)	821	(1,598)
Gain (loss) recognized in income	2,676	0	2,121	0			(96)	0	(96)	0	2,772	0	2,772	0
Gain (loss) recognized in income (ineffective portion)											0	0	(555)	0
Additional Derivative Instruments (Textual) [Abstract]
Hedging losses included in accumulated other comprehensive income			1,883
Notional amount of interest rate swap	$ 101,040		$ 101,040