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Note 9 - Convertible Debt (Details Textual) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Sep. 30, 2016 USD ($) $ / shares $ / item	Dec. 31, 2015 USD ($) $ / shares $ / item	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) $ / shares $ / item
Proceeds from Convertible Debt					$ 279,459
Payments for Call Options					22,540
Convertible Debt [Member]
Capped Call, Aggregate Call Options Purchased, Percentage Related to Shares Underlying the Convertible Note		100.00%				100.00%
Convertible Debt [Member] \| Convertible Notes 2015 [Member]
Debt Instrument, Face Amount		$ 230,000				$ 230,000
Debt Instrument, Interest Rate, Stated Percentage		1.125%				1.125%
Debt Instrument, Convertible, Conversion Ratio		24.8988
Debt Instrument, Convertible, Conversion Price \| $ / shares		$ 40.16				$ 40.16
Capped Call, Aggregate Call Options Purchased, Percentage Related to Shares Underlying the Convertible Note		100.00%				100.00%
Convertible Debt Holders in Default, Percent of Principal Amount		25.00%				25.00%
Convertible Debt in Default, Percent Holders to Declare Due and Payable		100.00%				100.00%
Convertible Debt in Bankruptcy, Insolvency, and Reorganization, Percent due and Payable		100.00%				100.00%
Proceeds from Convertible Debt						$ 230,000
Convertible Debt, Total		$ 175,974				175,974
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt		54,026
Debt Issuance Costs, Gross		6,359				6,359
Payments of Debt Issuance Costs		6,007
Unamortized Debt Issuance Expense		4,864				4,864
Debt Instrument, Convertible Equity Component Issuance Cost		$ 1,495				$ 1,495
Interest Expense, Debt, Total			14,396	13,574	12,853
Interest Expense, Debt, Excluding Amortization			2,587	2,588	2,577
Amortization of Debt Discount (Premium)			10,833	10,079	9,427
Amortization of Debt Issuance Costs			976	907	849
Derivative, Cap Price \| $ / item		52.06				52.06
Payments for Call Options						$ 17,802
Convertible Debt [Member] \| Convertible Notes 2015 [Member] \| Conversion Circumstance 1 [Member]
Debt Instrument, Convertible, Threshold Trading Days						20
Debt Instrument, Convertible, Threshold Consecutive Trading Days						30
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger						130.00%
Convertible Debt [Member] \| Convertible Notes 2015 [Member] \| Conversion Circumstance 2 [Member]
Debt Instrument, Convertible, Threshold Trading Days						5
Debt Instrument, Convertible, Threshold Consecutive Trading Days						5
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger						98.00%
Convertible Debt [Member] \| Convertible Notes 2016 [Member]
Debt Instrument, Face Amount	$ 287,500
Debt Instrument, Interest Rate, Stated Percentage	0.75%
Debt Instrument, Convertible, Conversion Ratio	17.7508
Debt Instrument, Convertible, Conversion Price \| $ / shares	$ 56.34
Capped Call, Aggregate Call Options Purchased, Percentage Related to Shares Underlying the Convertible Note	100.00%
Convertible Debt Holders in Default, Percent of Principal Amount	25.00%
Convertible Debt in Default, Percent Holders to Declare Due and Payable	100.00%
Convertible Debt in Bankruptcy, Insolvency, and Reorganization, Percent due and Payable	100.00%
Proceeds from Convertible Debt	$ 287,500
Convertible Debt, Total	216,775
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt	70,725
Debt Issuance Costs, Gross	5,798
Debt Instrument, Convertible Equity Component Issuance Cost	$ 1,891
Interest Expense, Debt, Total			16,741	15,742	4,553
Interest Expense, Debt, Excluding Amortization			2,156	2,154	651
Amortization of Debt Discount (Premium)			13,481	12,559	3,607
Amortization of Debt Issuance Costs			$ 1,104	$ 1,029	$ 295
Derivative, Cap Price \| $ / item	73.03
Payments for Call Options	$ 22,540
Debt Instrument, Repurchase Price, Percentage of Principal Amount Repurchased	100.00%
Debt and Equity Issuance Costs, Net	$ 7,689
Convertible Debt [Member] \| Convertible Notes 2016 [Member] \| Conversion Circumstance 1 [Member]
Debt Instrument, Convertible, Threshold Trading Days	20
Debt Instrument, Convertible, Threshold Consecutive Trading Days	30
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger	130.00%
Convertible Debt [Member] \| Convertible Notes 2016 [Member] \| Conversion Circumstance 2 [Member]
Debt Instrument, Convertible, Threshold Trading Days	5
Debt Instrument, Convertible, Threshold Consecutive Trading Days	5
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger	98.00%