Acquisitions (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Purchase price allocation
Goodwill	$ 233,599	$ 233,365	$ 220,013
Ascade
Purchase price allocation
Trade accounts receivable	3,049
Other current assets	2,701
Fixed assets	137
Acquired customer relationships and other intangible assets	5,640
Acquired technology assets	3,590
Goodwill	8,955
Total assets acquired	24,072
Accounts payable and accrued employee compensation	2,294
Deferred revenue	2,154
Other current liabilities	380
Total liabilities assumed	4,828
Net assets acquired	$ 19,244