Condensed Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Available-for-sale debt securities, amortized cost	$ 1,302,946	$ 1,199,409
Available-for-sale equity securities, amortized cost	$ 80,846	$ 77,152
Common stock, par value (in dollars per share)	$ 0.0002	$ 0.0002
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	30,330,675	29,988,460
Common stock, shares outstanding	30,330,675	29,988,460
Preferred stock par value (in dollars per share)	$ 0.00125	$ 0.00125
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0