Fair Value of Assets and Liabilities - Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Total	$ 163,202	$ 254,747
Fair value liabilities measured on recurring basis
Total	13,524	13,092
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair value assets measured on recurring basis
Total	154,288	225,387
Fair value liabilities measured on recurring basis
Total	10,015	10,377
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value assets measured on recurring basis
Total	8,914	29,360
Fair value liabilities measured on recurring basis
Total	3,509	2,715
Foreign exchange forward contracts | Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Foreign exchange forward contracts	217	1,382
Fair value liabilities measured on recurring basis
Derivative Liability	1,670	364
Foreign exchange forward contracts | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value assets measured on recurring basis
Foreign exchange forward contracts	217	1,382
Fair value liabilities measured on recurring basis
Derivative Liability	1,670	364
Interest rate swaps | Fair Value, Measurements, Recurring [Member]
Fair value liabilities measured on recurring basis
Derivative Liability	1,839	2,351
Interest rate swaps | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value liabilities measured on recurring basis
Derivative Liability	1,839	2,351
Certificates of deposit | Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Investments, Fair Value Disclosure	144,273	215,010
Certificates of deposit | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair value assets measured on recurring basis
Investments, Fair Value Disclosure	144,273	215,010
U.S. dollar indexed bond funds | Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Investments, Fair Value Disclosure	8,697	27,978
U.S. dollar indexed bond funds | Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair value assets measured on recurring basis
Investments, Fair Value Disclosure	8,697	27,978
Assets held in rabbi trusts [Member]
Fair value assets measured on recurring basis
Assets held in rabbi trusts	10,015	10,377
Assets held in rabbi trusts [Member] | Fair Value, Measurements, Recurring [Member]
Fair value assets measured on recurring basis
Assets held in rabbi trusts	10,015	10,377
Fair value liabilities measured on recurring basis
Deferred compensation	10,015	10,377
Assets held in rabbi trusts [Member] | Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair value assets measured on recurring basis
Assets held in rabbi trusts	10,015	10,377
Fair value liabilities measured on recurring basis
Deferred compensation	$ 10,015	$ 10,377