Note 8 - Convertible Debt (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Schedule of Long-term Debt Instruments [Table Text Block]

	December 31,			December 31,
	2019			2018
Principal	$	517,500		$	517,500
Less:
Unamortized debt discount		(38,105	)		(64,222	)
Unamortized debt issuance costs		(3,217	)		(5,453	)
Net carrying amount of long-term debt		476,178			447,825
Less current portion of long-term debt		217,467			—
Long-term debt, non-current portion	$	258,711		$	447,825

Convertible Debt [Table Text Block]

	Year Ended December 31,
	2019		2018		2017
Contractual interest expense	$	2,586	$	2,587	$	2,588
Amortization of debt discount		11,645		10,833		10,079
Amortization of debt issuance costs		1,050		976		907
Total interest expense	$	15,281	$	14,396	$	13,574

	Year Ended December 31,
	2019		2018		2017
Contractual interest expense	$	2,152	$	2,156	$	2,154
Amortization of debt discount		14,472		13,481		12,559
Amortization of debt issuance costs		1,186		1,104		1,029
Total interest expense	$	17,810	$	16,741	$	15,742