Fair Value of Financial Instruments (Details) (Recurring basis, Level 1, USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Fair Value of Financial Instruments
Total fair value of financial assets	$ 117,476	$ 42,471	$ 63,641
Money market funds
Fair Value of Financial Instruments
Total fair value of financial assets	117,451	42,446	63,616
Certificate of deposit
Fair Value of Financial Instruments
Total fair value of financial assets	$ 25	$ 25	$ 25

This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value on a recurring basis by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

No definition available.

Name:	us-gaap_AssetsFairValueDisclosureRecurring
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant