Convertible 3.75% Senior Notes (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Debt discount amortization	$ 8,643	$ 7,599	$ 6,680
Amortization of deferred financing costs	$ 943	$ 828	$ 1,132
Convertible Notes Payable
Debt Instrument [Line Items]
Stated interest rate	3.75%	3.75%	3.75%
Interest Expense at 3.75% coupon rate	$ 5,391	$ 5,391	$ 5,391
Debt discount amortization	8,643	7,599	6,680
Amortization of deferred financing costs	942	828	728
Less: capitalized interest and other	(3,778)	(514)	559
Total interest expense	$ 11,198	$ 13,304	$ 13,358