Credit Facilities (Details) (USD $)	0 Months Ended	12 Months Ended				0 Months Ended	5 Months Ended		0 Months Ended			12 Months Ended	0 Months Ended	12 Months Ended			0 Months Ended	12 Months Ended					0 Months Ended
	Dec. 10, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jun. 12, 2013	Dec. 03, 2013 Revolving Credit Facility Wells Fargo Bank	May 19, 2012 Revolving Credit Facility Wells Fargo Bank	Dec. 31, 2013 Revolving Credit Facility Wells Fargo Bank	Dec. 03, 2013 Revolving Credit Facility Wells Fargo Bank Six months ended June 30, 2013	Dec. 03, 2013 Revolving Credit Facility Wells Fargo Bank Nine months ended September 30, 2013	Dec. 03, 2013 Revolving Credit Facility Wells Fargo Bank Year ended December 31, 2013	Dec. 31, 2013 Revolving Credit Facility Wells Fargo Bank Year ended December 31, 2013	Dec. 03, 2013 Revolving Credit Facility Wells Fargo Bank Three months ending March 31, 2014	Dec. 31, 2013 Revolving Credit Facility Wells Fargo Bank Year ended December 31, 2014	Dec. 03, 2013 Revolving Credit Facility Wells Fargo Bank Prime Rate	Dec. 03, 2013 Letter of Credit Wells Fargo Bank	Dec. 10, 2013 Convertible Senior Notes 2.25% Convertible Senior Notes	Dec. 31, 2013 Convertible Senior Notes 2.25% Convertible Senior Notes	Dec. 31, 2013 Convertible Senior Notes 2.25% Convertible Senior Notes Minimum	Dec. 31, 2013 Convertible Senior Notes 2.25% Convertible Senior Notes Maximum	Dec. 10, 2013 Convertible Senior Notes 2.25% Convertible Senior Notes Other Assets	Dec. 10, 2013 Convertible Senior Notes 2.25% Convertible Senior Notes Additional Paid-in Capital	Dec. 10, 2013 Convertible Senior Notes 2.25% Convertible Senior Notes On or after December 15, 2016 D	Dec. 10, 2013 Convertible Senior Notes 2.25% Convertible Senior Notes Business Day Immediately Preceding September 15, 2018 Debt Instrument, Redemption, Scenario One D	Dec. 10, 2013 Convertible Senior Notes 2.25% Convertible Senior Notes Business Day Immediately Preceding September 15, 2018 Debt Instrument, Redemption, Scenario Two D
Line of Credit Facility [Line Items]
Convertible notes, face amount																	$ 86,250,000
Convertible notes, stated percentage																	2.25%
Proceeds from convertible debt		86,250,000	0	0													82,593,000
Convertible debt redemption, trading days threshold																							20	20
Convertible debt redemption, consecutive trading days threshold																							30 days	30 days
Convertible debt redemption, business days threshold																									5
Convertible debt redemption, consecutive business days threshold																									5 years
Convertible debt redemption, percentage of stock price trigger, percentage																							130.00%	130.00%	98.00%
Debt instrument, dedemption price, percentage																	100.00%						100.00%
Convertible debt, conversion ratio																	0.0416051
Convertible debt, conversion price																	$ 24.04
Debt instrument, debt default, declaration by note holders, percentage																	25.00%
Debt instrument, fair value																	66,900,000
Debt instrument, embedded conversion option																	19,300,000
Debt instrument, unamortized discount																	3,700,000				2,900,000	800,000
Interest expense, debt																		300,000
Accretion of debt discount																		200,000
Contractual coupon interest expense																		100,000
Amortization of debt issuance costs		(3,657,000)	0	0														21,000
Amortization of debt issuance costs, effective interest rate																		9.00%
Convertible notes		67,101,000	0															67,100,000
Deferred financing costs																		2,900,000
Estimated annual interest expense, debt																			5,700,000	6,900,000
Payments of derivative issuance costs	7,400,000
Derivative, cap price																	29.02
Line of credit facility, maximum borrowing capacity						20,000,000										6,000,000
Letters of credit outstanding, amount					5,400,000			5,400,000
Debt instrument, basis spread on variable rate															1.00%
Line of credit facility, unused capacity, commitment fee percentage							0.20%
Debt covenant, minimum current ratio						2.0
Debt covenant, maximum operating loss									9,000,000	13,000,000	14,500,000		1,500,000
Debt covenant, maximum capital expenditures												$ 6,000,000		$ 9,000,000