Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
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:	77,591	96,942
Recurring
Assets:
Total short-term investments	97,886
Recurring | Available-for-sale equity securities
Assets:
Short term investments:	77,591
Recurring | Corporate debt securities
Assets:
Short term investments:	19,525
Recurring | Mortgage-backed debt securities
Assets:
Short term investments:	209
Recurring | Mortgage-CMO debt securities
Assets:
Short term investments:	20
Recurring | Asset-backed debt securities
Assets:
Short term investments:	541
Recurring | Level 1
Assets:
Total short-term investments	77,270
Recurring | Level 1 | Available-for-sale equity securities
Assets:
Short term investments:	76,729
Recurring | Level 1 | Asset-backed debt securities
Assets:
Short term investments:	541
Recurring | Level 2
Assets:
Total short-term investments	20,616
Recurring | Level 2 | Available-for-sale equity securities
Assets:
Short term investments:	862
Recurring | Level 2 | Corporate debt securities
Assets:
Short term investments:	19,525
Recurring | Level 2 | Mortgage-backed debt securities
Assets:
Short term investments:	209
Recurring | Level 2 | Mortgage-CMO debt securities
Assets:
Short term investments:	$ 20