Convertible Senior Notes - Recognized Interest Expense (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Debt Instrument [Line Items]
Total	[1]	$ 12,916	$ 12,694	$ 25,757	$ 25,291
Convertible Debt [Member]
Debt Instrument [Line Items]
Contractual interest expense based on 0.50% per annum		1,653	1,672	3,306	3,325
Amortization of debt discount and issuance costs		11,868	11,322	23,598	22,511
Total		$ 13,521	$ 12,994	$ 26,904	$ 25,836
Effective interest rate of the liability component		4.70%	4.70%	4.70%	4.70%

[1] The Company capitalized $0.6 million and $0.3 million of interest expense related to properties under construction for the three months ended June 30, 2016 and 2015, respectively, and $1.1 million and $0.5 million for the six months ended June 30, 2016 and 2015, respectively.