UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Investments carried at fair value	$ 3,268	$ 3,279
Common stock, par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	96,000,000	96,000,000
Common stock, shares issued (in shares)	49,558,000	49,328,000
Common stock, shares outstanding (in shares)	49,558,000	49,328,000