Acquisitions (Details 1) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Additions to goodwill, client lists and other intangible assets resulting from acquisitions and contingent consideration earned on prior period acquisitions
Goodwill	$ 63,428	$ 35,647
Client lists [Member]
Additions to goodwill, client lists and other intangible assets resulting from acquisitions and contingent consideration earned on prior period acquisitions
Other intangible assets	43,095	12,129
Other intangibles assets [Member]
Additions to goodwill, client lists and other intangible assets resulting from acquisitions and contingent consideration earned on prior period acquisitions
Other intangible assets	$ 1,592	$ 512