Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value Measurements
Amount of transfers of financial assets between Level 1 and Level 2 measures	$ 0
Assets:
Short term investments:	117,218	200,577
Total short-term investments	117,200
Available-for-sale equity securities
Assets:
Short term investments:	96,942	174,610
Recurring
Assets:
Total short-term investments	117,218
Recurring | Available-for-sale equity securities
Assets:
Short term investments:	96,942
Recurring | Corporate debt securities
Assets:
Short term investments:	19,388
Recurring | Mortgage-backed debt securities
Assets:
Short term investments:	210
Recurring | Mortgage-CMO debt securities
Assets:
Short term investments:	20
Recurring | Asset-backed debt securities
Assets:
Short term investments:	658
Recurring | Level 1
Assets:
Total short-term investments	96,738
Recurring | Level 1 | Available-for-sale equity securities
Assets:
Short term investments:	96,080
Recurring | Level 1 | Asset-backed debt securities
Assets:
Short term investments:	658
Recurring | Level 2
Assets:
Total short-term investments	20,480
Recurring | Level 2 | Available-for-sale equity securities
Assets:
Short term investments:	862
Recurring | Level 2 | Corporate debt securities
Assets:
Short term investments:	19,388
Recurring | Level 2 | Mortgage-backed debt securities
Assets:
Short term investments:	210
Recurring | Level 2 | Mortgage-CMO debt securities
Assets:
Short term investments:	$ 20