Operating Segments and Related Information (Details 4) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue	$ 434,366	$ 375,366	$ 369,380	$ 351,542	$ 400,319	$ 358,141	$ 389,329	$ 348,583	$ 1,530,654	$ 1,496,372	$ 1,405,358
United States
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue									763,905	755,640	717,841
Europe [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue									350,924	370,800	337,163
Other Geographic Region [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue									$ 415,825	$ 369,932	$ 350,354