Stock Options - Summary of Plans (Details)							12 Months Ended
	May. 17, 2012 shares	May. 19, 2011 shares	May. 20, 2010 shares	May. 21, 2009 shares	May. 29, 2008 shares	May. 30, 2007 shares	Dec. 31, 2015 item shares	Mar. 19, 2015 shares	Dec. 31, 2014 shares	Dec. 31, 2013 shares	Mar. 17, 2005 shares
Stock Options
Number of stock-based compensation plans | item							2
Options outstanding (in shares)							2,598,000		3,076,000	3,045,000
2005 Plan
Stock Options
Shares available for issuance	3,700,000	3,400,000	3,000,000	2,500,000		1,500,000					750,000
Additional increase in number of shares available for issuance	300,000	400,000	500,000	500,000	500,000	750,000
Options exercised (in shares)							632,835
Options outstanding (in shares)							2,595,334
Options granted (in shares)							3,892,000
Options cancelled (in shares)							663,831
2015 Plan
Stock Options
Shares available for issuance								600,000
Options outstanding (in shares)							3,000
Options granted (in shares)							3,000
Options cancelled (in shares)							0
Shares available for future grant							597,000
Number of Equity Incentive Programs | item							3
Shares issued pursuant to the Stock Issuance Program							0
2015 Plan | Non-employee Board member
Stock Options
Options that will be granted upon initial election or appointment to the Board (in shares)							10,000
Preceding period within which individual has not previously been employed by the company							3 months
Options that will be granted to purchase shares of common stock on the date of each annual stockholders meeting							8,000
Period for which individual should serve as a non-employee Board member							3 months