Convertible Notes (Narrative) (Detail) $ / shares in Units, shares in Millions						3 Months Ended	9 Months Ended
	Nov. 21, 2016 USD ($)	Nov. 20, 2015 USD ($)	Feb. 11, 2014 USD ($)	Feb. 05, 2014 USD ($)	May 16, 2011	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Nov. 23, 2016 USD ($)	Nov. 22, 2016 USD ($) $ / shares	Nov. 21, 2015 USD ($)	Feb. 12, 2014 USD ($) $ / shares	Feb. 06, 2014 USD ($) $ / shares
Debt Instrument [Line Items]
Principal amount a $5 incentive cash payment per each to convert debt						$ 1,000	$ 1,000
Convertible note rate conversion trading days (in days)						0	0
Convertible Notes rate conversion consecutive trading days (in days)						30	$ 30
Minimum conversion price percent for note conversion (in Percent)							130.00%
Convertible notes repurchase price as a percentage of principal (in Percent)					100.00%
Interest Paid							$ 7,224,000	$ 9,930,000
Share Price | $ / shares														$ 7.97
February 2018 Notes [Member]
Debt Instrument [Line Items]
Convertible notes		$ 246,400,000				124,922,000	124,922,000		$ 121,595,000		$ 126,400,000		$ 300,000,000
Debt instrument, interest rate (in Percent)													4.00%
Unamortized discount of liability component		(3,100,000)				$ (1,525,000)	$ (1,525,000)		(4,852,000)	$ (4,600,000)	(4,300,000)	$ (14,100,000)	$ (29,700,000)
Deferred issuance costs		900,000								$ 1,400,000	1,300,000	$ 4,100,000
Purchase call option unwind		270,000
Warrant unwind		170,000
Fees and Commissions, Transfer Agent		100,000
Debt discount recorded to additional paid in capital													19,300,000
Debt discount recorded to deferred tax liability													$ 10,400,000
Minimum conversion price percent for note conversion (in Percent)						130.00%
Maximum percent of common stock closing price and conversion rate to convert note (in Percent)						98.00%
Debt Instrument, Interest Rate, Effective Percentage													6.90%
Convertible notes, conversion price (in Dollars per Share) | $ / shares													$ 9.17
Estimated market interest rate for similar nonconvertible instrument													7.00%
Debt instrument, convertible, remaining amortization period (in Duration)							4 months 4 days
Net proceeds from the issuance of convertible notes			$ 290,200,000
Debt Instrument, Repurchase Amount		53,600,000									120,000,000
Debt instrument, repurchase amount paid		43,700,000									121,500,000
Interest Paid	$ 1,500,000
Debt Instrument, Face Amount						$ 126,447,000	$ 126,447,000		126,447,000
Conversion Rate per $1,000 Principal Amount (in Ratio)			109.1048
Gain on conversion of convertible notes		(6,500,000)
Dividends Payable, Amount Per Share | $ / shares						$ 0.15	$ 0.15
February 2018 Note Warrant [Member]
Debt Instrument [Line Items]
Convertible notes, conversion price (in Dollars per Share) | $ / shares						$ 10.3610	$ 10.3610
Proceeds from Issuance of Warrants				$ 11,400,000
December 2021 Notes [Member]
Debt Instrument [Line Items]
Convertible notes		$ 150,000,000				$ 115,716,000	$ 115,716,000		110,848,000		$ 150,000,000
Debt instrument, interest rate (in Percent)											2.80%
Unamortized discount of liability component						(34,284,000)	$ (34,284,000)		(39,152,000)		$ (4,300,000)
Debt discount recorded to additional paid in capital											23,800,000
Debt discount recorded to deferred tax liability											$ 12,800,000
Maximum percent of common stock closing price and conversion rate to convert note (in Percent)							98.00%
Debt Instrument, Interest Rate, Effective Percentage											3.40%
Convertible notes, conversion price (in Dollars per Share) | $ / shares											$ 3.81
Estimated market interest rate for similar nonconvertible instrument											9.50%
Debt instrument, convertible, remaining amortization period (in Duration)							4 years 2 months 3 days
Net proceeds from the issuance of convertible notes	$ 145,700,000
Debt Instrument, Face Amount						$ 150,000,000	$ 150,000,000		$ 150,000,000
Conversion Rate per $1,000 Principal Amount (in Ratio)	262.2951
Proceeds from Issuance of Warrants	$ 14,400,000
February 2018 Note Purchase Call Option [Member]
Debt Instrument [Line Items]
Purchased call options cost			$ 31,000,000
Number of shares of common stock covered by the purchased call options purchased (in Shares) | shares						13.8	13.8
Deferred taxes included in purchased call options cost			$ 10,800,000
Purchased Call Options [Member]
Debt Instrument [Line Items]
Convertible notes, conversion price (in Dollars per Share) | $ / shares						$ 4.88	$ 4.88
Series 2012 Notes [Member]
Debt Instrument [Line Items]
Convertible notes														$ 131,700,000