Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
Stockholders' equity:
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	41,089,720	42,711,016
Common stock, outstanding (in shares)	41,089,720	42,711,016