Condensed Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Available-for-sale debt securities, amortized cost	$ 1,054,902	$ 1,008,662
Trading securities, debt, amortized cost	3,800	3,801
Available-for-sale equity securities, amortized cost	$ 80,464	$ 75,318
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	29,866,705	29,696,682
Common stock, shares outstanding	29,866,705	29,696,682
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