Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value Measurements
Amount of transfers of financial assets between Level 1 and Level 2 measures	$ 0
Assets:
Short term investments:	35,020	117,218
Equity Securities
Assets:
Short term investments:	35,002	96,942
Fair Value, Measurements, Recurring
Assets:
Total short-term investments	35,020
Fair Value, Measurements, Recurring | Equity Securities
Assets:
Short term investments:	35,002
Fair Value, Measurements, Recurring | Collateralized Debt Obligations
Assets:
Short term investments:	18
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Assets:
Total short-term investments	35,002
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Equity Securities
Assets:
Short term investments:	35,002
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets:
Total short-term investments	18
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Collateralized Debt Obligations
Assets:
Short term investments:	$ 18