CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current assets
Accounts receivable, allowance	$ 2,434	$ 2,203
Employee loans, current, allowance	0	0
Noncurrent assets
Employee loans, long-term, allowance	$ 0	$ 0
Stockholders' equity
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	160,000,000	160,000,000
Common stock, shares issued (in shares )	46,914,858	45,398,523
Common stock, shares outstanding (in shares)	45,958,829	44,442,494