Long-Term Obligations and Commitments, Long-Term Obligations (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Long-Term Obligations [Abstract]
Total long-term obligations, including current portion	$ 607,477	$ 589,105
Less: current portion	(1,621)	(1,185)
Total Long-Term Obligations	605,856	587,920
1 Percent Convertible Senior Notes [Member]
Long-Term Obligations [Abstract]
Total long-term obligations, including current portion	533,111	500,511
Long-term Mortgage Debt [Member]
Long-Term Obligations [Abstract]
Total long-term obligations, including current portion	59,771	0
Long-term Financing Liability for Leased Facility [Member]
Long-Term Obligations [Abstract]
Total long-term obligations, including current portion	0	72,359
Fixed Rate Note with Morgan Stanley [Member]
Long-Term Obligations [Abstract]
Total long-term obligations, including current portion	12,500	12,500
Leases and Other Obligations [Member]
Long-Term Obligations [Abstract]
Total long-term obligations, including current portion	$ 2,095	$ 3,735