Goodwill and Intangible Assets - Goodwill (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Goodwill [Line Items]
Accumulated impairment loss	$ 8,344
Goodwill [Roll Forward]
Goodwill balance at January 1	175,108	61,144
Adjustment related to previous acquisitions	381	280
Additions as the result of acquisitions	9,016	113,684
Goodwill balance at December 31	$ 184,505	$ 175,108