Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Available-for-sale securities, amortized cost	$ 1,709,100	$ 1,761,289
Trading securities, amortized cost	12,699	11,277
Equity securities, amortized cost	63,708	64,819
Allowance for doubtful accounts	1,125	785
Property and equipment accumulated depreciation	$ 40,856	$ 39,894
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	75,000,000	75,000,000
Common stock, shares issued (in shares)	25,167,822	25,097,408
Common stock, shares outstanding (in shares)	25,167,822	25,097,408