Long-Term Debt - Convertible Notes Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Long-Term Debt
Cash interest per contractual coupon rate	$ 4,269	$ 5,033	$ 13,227	$ 14,496
Convertible Senior Notes 1.00 percent due 2020 [Member]
Long-Term Debt
Cash interest per contractual coupon rate	719	719	2,157	2,156
Amortization of note discount	2,439	2,313	7,219	6,850
Amortization of debt issuance costs	159	142	463	413
Total interest expense related to Convertible Notes	$ 3,317	$ 3,174	$ 9,839	$ 9,419