Long-Term Debt, Cash Convertible Notes (Details)		3 Months Ended	9 Months Ended
	Jul. 16, 2013 USD ($) $ / shares	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($) TradingDay d	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Jul. 31, 2013 $ / shares
Debt Instrument [Line Items]
Interest expense related to amortization of debt discount			$ 5,941,000	$ 5,618,000
1.50% Cash Convertible Senior Notes Due 2018 [Member]
Debt Instrument [Line Items]
Aggregate principal of convertible notes	$ 150,000,000
Interest rate for notes	1.50%
Consecutive trading days | d			30
Trading price condition (in dollars per share) | $ / shares	$ 25.30
Initial cash conversion rate	51.3769
Par amount of convertible note	$ 1,000
Initial conversion price (in dollars per share) | $ / shares	$ 19.4640
Deferred loan costs	$ 3,900,000
Fair value of cash conversion derivative	$ 36,800,000
Interest expense related to amortization of debt discount		$ 2,000,000	$ 5,900,000
Effective interest rate		5.70%	5.70%
Debt instrument, unamortized discount		$ 6,200,000	$ 6,200,000		$ 12,100,000
Warrants strike price (in dollars per share) | $ / shares						$ 25.95
Conversion price premium percentage						60.00%
1.50% Cash Convertible Senior Notes Due 2018 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Number of trading days | TradingDay			20