Fair Value Measurements (Details) (Fair value on a recurring basis, USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair Value Measurements
Total nonfinancial assets measured at fair value	$ 0
Total nonfinancial liabilities measured at fair value	0
Fair value
Fair Value Measurements
Total assets measured at fair value	23,102	10,315
Fair value | Cash and cash equivalents
Fair Value Measurements
Total assets measured at fair value	23,102	10,315
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value Measurements
Total assets measured at fair value	23,102	10,315
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Fair Value Measurements
Total assets measured at fair value	$ 23,102	$ 10,315