Fair Value of Assets and Liabilities - Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Assets held in a rabbi trust	$ 6,893	$ 7,170
Total	281,712	296,216
Fair value liabilities measured on recurring basis
Deferred compensation	6,893	7,170
Total	11,761	12,949
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair value assets measured on recurring basis
Assets held in a rabbi trust	6,893	7,170
Total	252,882	276,203
Fair value liabilities measured on recurring basis
Deferred compensation	6,893	7,170
Total	6,893	7,170
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value assets measured on recurring basis
Assets held in a rabbi trust	0	0
Total	28,830	20,013
Fair value liabilities measured on recurring basis
Deferred compensation	0	0
Total	4,868	5,779
Forward Contracts [Member] | Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Foreign exchange forward contracts	3,960	2,193
Fair value liabilities measured on recurring basis
Fair value Liabilities measured on recurring basis- Derivatives	1,135	1,983
Forward Contracts [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair value assets measured on recurring basis
Foreign exchange forward contracts	0	0
Fair value liabilities measured on recurring basis
Fair value Liabilities measured on recurring basis- Derivatives	0	0
Forward Contracts [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value assets measured on recurring basis
Foreign exchange forward contracts	3,960	2,193
Fair value liabilities measured on recurring basis
Fair value Liabilities measured on recurring basis- Derivatives	1,135	1,983
Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member]
Fair value liabilities measured on recurring basis
Fair value Liabilities measured on recurring basis- Derivatives	3,733	3,796
Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair value liabilities measured on recurring basis
Fair value Liabilities measured on recurring basis- Derivatives	0	0
Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value liabilities measured on recurring basis
Fair value Liabilities measured on recurring basis- Derivatives	3,733	3,796
Certificates Of Deposit [Member] | Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Investments, Fair Value Disclosure	245,989	269,033
Certificates Of Deposit [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair value assets measured on recurring basis
Investments, Fair Value Disclosure	245,989	269,033
Certificates Of Deposit [Member] | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value assets measured on recurring basis
Investments, Fair Value Disclosure	0	0
U.S. dollar indexed bond funds [Member] | Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Investments, Fair Value Disclosure	24,870	17,820
U.S. dollar indexed bond funds [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair value assets measured on recurring basis
Investments, Fair Value Disclosure	0	0
U.S. dollar indexed bond funds [Member] | Level 2 [Member]
Fair value assets measured on recurring basis
Investments, Fair Value Disclosure	$ 24,870	$ 17,820