CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Balances at Dec. 31, 2010	$ 23,106	$ 191,343		$ 69	$ (168,306)
Balances (in shares) at Dec. 31, 2010		52,957,787
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options	7,588	7,588
Issuance of common stock upon exercise of options (in shares)		2,379,116
Issuance of common stock under employee stock purchase plan	711	711
Issuance of common stock under employee stock purchase plan (in shares)		169,217
Stock-based compensation	3,869	3,869
Net income (loss)	70,726				70,726
Unrealized gain (loss) on available-for-sale securities	(82)			(82)
Balances at Dec. 31, 2011	105,918	203,511		(13)	(97,580)
Balances (in shares) at Dec. 31, 2011		55,506,120
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options	1,835	1,835
Issuance of common stock upon exercise of options (in shares)	628,394	628,394
Issuance of common stock under employee stock purchase plan	851	851
Issuance of common stock under employee stock purchase plan (in shares)	203,389	203,389
Issuance of common stock in conjunction with vesting of restricted stock units	278	278
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)		45,810
Stock-based compensation	4,791	4,791
Net income (loss)	(29,781)				(29,781)
Unrealized gain (loss) on available-for-sale securities	44			44
Balances at Dec. 31, 2012	83,936	211,266		31	(127,361)
Balances (in shares) at Dec. 31, 2012	56,383,713	56,383,713
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options	2,782	2,782
Issuance of common stock upon exercise of options (in shares)	621,090	621,090
Issuance of common stock under employee stock purchase plan	966	966
Issuance of common stock under employee stock purchase plan (in shares)	222,062	222,062
Issuance of common stock in conjunction with vesting of restricted stock units	765	765
Issuance of common stock in conjunction with vesting of restricted stock units (in shares)		142,818
Stock-based compensation	5,345	5,345
Windfall tax benefit	347		347
Net income (loss)	43,313				43,313
Unrealized gain (loss) on available-for-sale securities	(38)			(38)
Balances at Dec. 31, 2013	$ 137,416	$ 221,124	$ 347	$ (7)	$ (84,048)
Balances (in shares) at Dec. 31, 2013	57,369,683	57,369,683