Note 9 - Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

Notes Tables

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]

	Fair Value Measurements Using
December 31, 2018	Fair Value		Quoted Prices in Active Markets For Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash and cash equivalents	$	43,247	$	43,247	$	–	$	–
Restricted cash and cash equivalents		11,673		11,673		–		–
Marketable equity securities		140,223		140,223		–		–
Corporate debt securities		67,632		47,921		19,711		–
Asset–backed securities		62,068		–		62,068		–
U.S. Treasury securities		21,457		21,457		–		–
State and municipal securities		21,436		–		21,436		–
Total financial assets	$	367,736	$	264,521	$	103,215	$	–

	Fair Value Measurements Using
December 31, 2017	Fair Value		Quoted Prices in Active Markets For Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Cash and cash equivalents	$	59,118	$	59,118	$	–	$	–
Restricted cash and cash equivalents		8,303		8,303		–		–
Marketable equity securities		139,085		139,085		–		–
Corporate debt securities		65,461		43,073		22,388		–
Asset–backed securities		53,544		–		53,544		–
U.S. Treasury securities		21,172		21,172		–		–
State and municipal securities		26,218		–		26,218		–
Total financial assets	$	372,901	$	270,751	$	102,150	$	–