CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Valuation allowance	$ 47,706	$ 47,121
Common stock, shares authorized (in shares)	90,000,000	90,000,000
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares issued (in shares)	25,294,582	25,194,903
Common stock, shares outstanding (in shares)	25,126,537	25,025,933
Treasury stock, at cost	168,045	168,970