Obligations Long-term debt obligations, Maturities of principal of long-term debt, and Interest Cost (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jun. 03, 2019	Mar. 31, 2015
Debt Instrument [Line Items]
Current portion of long-term debt	$ 94,170,000	$ 0
Long-term net carrying amount of Senior Convertible Notes	350,588,000	317,377,000
2020	94,909,000
2021	0
2022	0
2023	0
2024	400,000,000
2025	0
Total	494,909,000
Amortization of financing costs	1,500,000	1,400,000	$ 1,400,000
Convertible Notes 2020 and 2024
Debt Instrument [Line Items]
Unamortized interest discount	(65,393,000)	(15,428,000)
Deferred financing costs	(5,859,000)	(1,621,000)
Total net carrying amount of Senior Convertible Notes	423,657,000	298,951,000
Current portion of long-term debt	94,170,000	0
Long-term net carrying amount of Senior Convertible Notes	329,487,000	298,951,000
Convertible Debt
Debt Instrument [Line Items]
Contractual coupon interest	7,424,000
Accretion of debt discount	15,065,000
Amortization of financing costs	1,475,000
Total	23,964,000
Convertible Debt | Convertible Notes 2020
Debt Instrument [Line Items]
Debt instrument face amount	94,909,000	316,000,000			$ 316,000,000.0
Contractual coupon interest	2,824,000	4,740,000	4,740,000
Accretion of debt discount	7,743,000	12,434,000	11,715,000
Amortization of financing costs	821,000	1,390,000	1,390,000
Total	11,388,000	18,564,000	$ 17,845,000
Convertible Debt | Convertible Notes 2024
Debt Instrument [Line Items]
Debt instrument face amount	400,000,000	$ 0		$ 400,000,000.0
Deferred financing costs				$ (1,700,000)
Contractual coupon interest	4,600,000
Accretion of debt discount	7,322,000
Amortization of financing costs	654,000
Total	$ 12,576,000