Note 9 - Convertible Debt

3 Months Ended

Mar. 31, 2019

Convertible Debt [Member]

Notes to Financial Statements

Debt Disclosure [Text Block]

9.

Convertible debt 

The carrying amount of the Company’s long-term debt consists of the following:

	March 31, 2019			December 31, 2018
Principal	$	517,500		$	517,500
Less:
Unamortized debt discount		(57,959	)		(64,222	)
Unamortized debt issuance costs		(4,917	)		(5,453	)
Net carrying amount of long-term debt		454,624			447,825
Less current portion of long-term debt		—			—
Long-term debt, non-current portion	$	454,624		$	447,825

In

December 2015,

the Company issued 

$230,000

 of

1.125%

convertible senior notes due

2020

(the “Convertible Notes

2015”

). The Convertible Notes

2015

will mature

December 1, 2020,

unless earlier converted or repurchased. Interest on the Convertible Notes

2015

is payable on

June 1

and

December 1

of each year, beginning on

June 1, 2016.

The initial conversion rate is 

24.8988

 shares of common stock per

$1

principal amount of Convertible Notes

2015,

which represents an initial conversion price of approximately 

$40.16

 per share. The total interest expense recognized for the

three

months ended

March 31, 2019

was

$3,681,

which consists of

$640

of contractual interest expense,

$2,790

of amortization of debt discount and

$251

of amortization of debt issuance costs. The total interest expense recognized for the

three

months ended

March 31, 2018

was

$3,469,

which consists of

$640

of contractual interest expense,

$2,595

of amortization of debt discount and

$234

of amortization of debt issuance costs.

In connection with the issuance of the Convertible Notes

2015,

the Company entered into capped call transactions (the “Capped Call

2015”

) in private transactions. Under the Capped Call

2015,

the Company purchased capped call options that in aggregate relate to 

100%

 of the total number of shares of the Company's common stock underlying the Convertible Notes

2015,

with a strike price equal to the conversion price of the Convertible Notes

2015

and with a cap price equal to 

$52.06

 per share.

In

September 2016,

the Company issued

$287,500

of

0.75%

convertible senior notes due

2021

(the “Convertible Notes

2016”,

and together with the Convertible Notes

2015,

the “Convertible Notes”). The Convertible Notes

2016

will mature on

September 1, 2021,

unless earlier converted or repurchased. Interest on the Convertible Notes

2016

is payable on

March 1

and

September 1

of each year, beginning on

March 1, 2017.

The initial conversion rate is

17.7508

shares of common stock per

$1

principal amount of the Convertible Notes

2016,

which represents an initial conversion price of approximately

$56.34

per share.  The total interest expense recognized for the

three

months ended

March 31, 2019

was

$4,291,

which consists of

$533

of contractual interest expense,

$3,473

of amortization of debt discount and

$285

of amortization of debt issuance costs. The total interest expense recognized for the

three

months ended

March 31, 2018

was

$4,034,

which consists of

$533

of contractual interest expense,

$3,236

of amortization of debt discount and

$265

of amortization of debt issuance costs.

In connection with the issuance of the Convertible Notes

2016,

the Company entered into capped call transactions (the “Capped Call

2016”

) in private transactions. Under the Capped Call

2016,

the Company purchased capped call options that in aggregate relate to

100%

of the total number of shares of the Company's common stock underlying the Convertible Notes

2016,

with a strike price approximately equal to the conversion price of the Convertible Notes

2016

and with a cap price equal to approximately

$73.03

per share.