Convertible Notes (Details 3) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Interest expense related to notes
Amortization of discount and debt issuance costs	$ 1,678	$ 2,680
Interest expense	2,271	4,421
1.125% Convertible Senior Notes due 2018
Interest expense related to notes
Interest	0	53
Amortization of discount and debt issuance costs	$ 0	1,090
Convertible Notes Payable [Member]
Interest expense related to notes
Interest expense		$ 3,326
Convertible Notes Payable [Member] \| Senior, One Point Three Seven Five Percent Convertible Notes Due Two Thousand Twenty Three [Member] [Member]
Interest expense related to notes
Convertible notes stated interest rate (as a percent)	1.375%	1.375%
Debt Instrument, Interest Rate, Effective Percentage	4.90%	4.90%
Convertible Notes Payable [Member] \| 1.125% Convertible Senior Notes due 2018
Interest expense related to notes
Debt Instrument, Interest Rate, Effective Percentage		5.50%
Convertible Senior Notes \| Senior, One Point Three Seven Five Percent Convertible Notes Due Two Thousand Twenty Three [Member] [Member]
Interest expense related to notes
Interest	$ 593	$ 593
Amortization of discount and debt issuance costs	$ 1,678	$ 1,590
Convertible Notes Payable [Member] \| 1.125% Convertible Senior Notes due 2018
Interest expense related to notes
Convertible notes stated interest rate (as a percent)		1.125%

Amount of amortization expense attributable to debt discount (premium) and debt issuance costs.

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