Note 10 - Fair Value Measurement - Schedule of Carrying and Fair Value Amounts (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Fair Value, Inputs, Level 1 [Member] | Reported Value Measurement [Member]
Held-to-maturity marketable securities		$ 47,918	$ 66,100	$ 81,103
Convertible notes		0	0	69,659
Fair Value, Inputs, Level 1 [Member] | Estimate of Fair Value Measurement [Member]
Held-to-maturity marketable securities		47,856	65,290	79,941
Convertible notes		0	0	69,472
Fair Value, Inputs, Level 3 [Member] | Reported Value Measurement [Member] | Revolving Credit Facility [Member]
Credit Agreement - revolving credit facility	[1]	250,000	197,000	137,000
Fair Value, Inputs, Level 3 [Member] | Reported Value Measurement [Member] | The 2019 Notes [Member]
Notes	[1]	0	40,000	80,000
Fair Value, Inputs, Level 3 [Member] | Reported Value Measurement [Member] | Term Loan [Member]
Notes	[1]	140,625	146,250	148,125
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member] | Revolving Credit Facility [Member]
Credit Agreement - revolving credit facility	[1]	251,986	197,889	137,636
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member] | The 2019 Notes [Member]
Notes	[1]	0	40,484	82,191
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member] | Term Loan [Member]
Notes	[1]	$ 141,634	$ 147,141	$ 148,832

[1] See Note 13 for definitions of, and more information about, the 2019 Notes and Credit Agreement.