Fair Value Measurements (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fair Value Measurements
Amount of transfers of financial assets between Level 1 and Level 2 measures	$ 0
Available-for-sale equity securities
Assets:
Short term investments:	33,205	$ 35,002
Recurring
Assets:
Total short-term investments	33,222
Recurring | Available-for-sale equity securities
Assets:
Short term investments:	33,205
Recurring | Mortgage-CMO debt securities
Assets:
Short term investments:	17
Recurring | Level 1
Assets:
Total short-term investments	33,205
Recurring | Level 1 | Available-for-sale equity securities
Assets:
Short term investments:	33,205
Recurring | Level 2
Assets:
Total short-term investments	17
Recurring | Level 2 | Mortgage-CMO debt securities
Assets:
Short term investments:	$ 17