Long-Term Debt Senior Convertible Notes (Details)		3 Months Ended	9 Months Ended
	Aug. 12, 2016 USD ($)	Sep. 30, 2017 USD ($) $ / shares	Sep. 30, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Senior Convertible Notes, net carrying amount		$ 137,012,000	$ 137,012,000	$ 130,856,000
Capped Call, cap price | $ / shares		$ 60.00	$ 60.00
1.50% Senior Convertible Notes Due 2021 [Member]
Debt Instrument [Line Items]
Senior Convertible Notes, face amount		$ 172,500,000	$ 172,500,000	172,500,000
Senior Convertible Notes, interest rate, stated percentage		1.50%	1.50%
Senior Convertible Notes, conversion ratio			24.6914
Senior Convertible Notes, principal amount of note		$ 1,000	$ 1,000
Senior Convertible Notes, conversion price | $ / shares		$ 40.50	$ 40.50
Senior Convertible Notes, initial fair value of liability component	$ 132,300,000
Senior Convertible Notes, comparable yield	7.25%
Senior Convertible Notes, initial value of equity component	$ 40,200,000
Interest Expense, Senior Convertible Notes		$ 2,500,000	$ 7,400,000
Senior Convertible Notes, unamortized debt discount		32,048,000	32,048,000	37,513,000
Unamortized deferred financing costs		(3,440,000)	(3,440,000)	(4,131,000)
Senior Convertible Notes, net carrying amount		$ 137,012,000	$ 137,012,000	$ 130,856,000