Note 4 - Fair Value Measurement (Details) - Financial Assets and Liabilities, Fair Value - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Assets:
Fair value of assets	$ 190,386,000	$ 180,155,000
Liabilities:
Contingent consideration	0	2,507,000
Total		2,507,000
Money Market Funds [Member]
Assets:
Fair value of assets	31,640,000	60,078,000
Certificates of Deposit [Member]
Assets:
Fair value of assets	21,574,000	22,778,000
US Government Agencies Short-term Debt Securities [Member]
Assets:
Fair value of assets	123,532,000	89,674,000
Auction Rate Securities [Member]
Assets:
Fair value of assets	5,361,000	5,389,000
Equity Funds [Member]
Assets:
Fair value of assets	8,279,000	2,236,000
Fair Value, Inputs, Level 1 [Member]
Assets:
Fair value of assets	39,919,000	62,314,000
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Assets:
Fair value of assets	31,640,000	60,078,000
Fair Value, Inputs, Level 1 [Member] | Equity Funds [Member]
Assets:
Fair value of assets	8,279,000	2,236,000
Fair Value, Inputs, Level 2 [Member]
Assets:
Fair value of assets	145,106,000	112,452,000
Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member]
Assets:
Fair value of assets	21,574,000	22,778,000
Fair Value, Inputs, Level 2 [Member] | US Government Agencies Short-term Debt Securities [Member]
Assets:
Fair value of assets	123,532,000	89,674,000
Fair Value, Inputs, Level 3 [Member]
Assets:
Fair value of assets	5,361,000	5,389,000
Liabilities:
Contingent consideration		2,507,000
Total		2,507,000
Fair Value, Inputs, Level 3 [Member] | Auction Rate Securities [Member]
Assets:
Fair value of assets	$ 5,361,000	$ 5,389,000