Fair Values of Financial Instruments Schedule of Fair Values of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Assets
Cash and cash equivalents	$ 101,561	$ 136,411	$ 154,438	$ 133,086
Cash and cash equivalents, at fair value	101,561	136,411
Foreign exchange forwards, asset	185	146
Liabilities
Line of Credit Facility, Amount Outstanding	125,000
Foreign exchange forwards, liability	357	114
Interest Rate Swaps	2,817	2,725
USD Denominated Term Loan [Member]
Liabilities
Term loans	273,750	277,500
Term loans, at fair value	271,862	275,365
Line of Credit [Member]
Liabilities
Line of Credit Facility, Amount Outstanding	125,000	140,000
Line of Credit Facility, Fair Value of Amount Outstanding	123,996	138,751
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets
Foreign exchange forwards, asset, at fair value	185	146
Liabilities
Foreign exchange forwards, liability, at fair value	357	114
Interest Rate Derivative Liabilities, at Fair Value	$ 2,817	$ 2,725