Consolidated Balance Sheets (Parenthetical) (Unaudited) - $ / shares	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Common stock, authorized (in shares)	100,000,000	100,000,000	100,000,000
Common stock, shares issued (in shares)	41,942,593	42,711,016	42,930,905
Common stock, outstanding (in shares)	41,942,593	42,711,016	42,930,905