Convertible Notes (Narrative) (Detail) $ / shares in Units, shares in Millions			2 Months Ended	3 Months Ended			12 Months Ended
	Sep. 18, 2019 USD ($)	Nov. 21, 2016 USD ($)	Nov. 18, 2019 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 12, 2019 shares	Sep. 17, 2019 USD ($) $ / shares	Nov. 22, 2016 USD ($) $ / shares	Nov. 20, 2015 USD ($)
Debt Instrument [Line Items]
Exchange of debt				$ 86,100,000
Cash paid per round lot to exchange debt									$ 70.00
Cash paid to exchange convertible note									6,000,000
Debt Instrument, Face Amount				14,805,000
Round lot of notes									$ 1,000
Net receipts for capped call transactions						$ 0
Gain on conversion of convertible notes				606,000	$ 3,900,000	$ 0
December 2021 Notes [Member]
Debt Instrument [Line Items]
Payment for Debt Extinguishment or Debt Prepayment Cost				6,000,000			$ 39,900,000
Stock Issued During Period, Shares, Other | shares							3.5
Convertible notes				12,402,000			$ 16,950,000			$ 150,000,000	$ 150,000,000
Debt Instrument, Interest Rate, Stated Percentage										2.75%
Unamortized discount of liability component				(1,403,000)			(2,220,000)			$ (4,300,000)
Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature	$ 13,500,000
Convertible note rate conversion trading days (in days)				0
Convertible Notes rate conversion consecutive trading days (in days)				$ 30
Debt discount recorded to additional paid in capital										23,800,000
Debt discount recorded to deferred tax liability										$ 12,800,000
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										9.70%
Convertible notes, conversion price (in Dollars per Share) | $ / shares										$ 3.81
Cap Price capped call | $ / shares										$ 4.88
Capped call unwind shares repurchased | shares								1.6
Estimated market interest rate for similar nonconvertible instrument										9.50%
Debt instrument, convertible, remaining amortization period (in Duration)				1 year 8 months 5 days
Extinguishment of Debt, Amount				$ 5,400,000			44,800,000
Net proceeds from the issuance of convertible notes		$ 145,700,000
Debt Instrument, Face Amount				13,805,000			19,170,000
Net receipts for capped call transactions		$ 14,400,000
Gain on conversion of convertible notes				(100,000)			(2,500,000)
December 2024 Notes [Member]
Debt Instrument [Line Items]
Payment for Debt Extinguishment or Debt Prepayment Cost				$ 12,900,000			$ 58,000,000
Stock Issued During Period, Shares, Other | shares							9.9
Debt Instrument, Interest Rate, Stated Percentage									2.75%
Debt instrument, accretion rate				2.375%
Unamortized discount of liability component				$ (100,000)			$ (1,200,000)		$ (9,400,000)
Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature	$ 8,100,000			8,100,000
Adjustments to Additional Paid in Capital, Other				$ 1,300,000
Debt discount recorded to additional paid in capital									5,500,000
Debt discount recorded to deferred tax liability									$ 1,200,000
Maximum percent of common stock closing price and conversion rate to convert note (in Percent)				98.00%
Debt Instrument, Interest Rate, Effective Percentage				7.50%
Convertible notes, conversion price (in Dollars per Share) | $ / shares									$ 3.81
Cap Price capped call | $ / shares									$ 4.88
Capped call unwind shares repurchased | shares								1.6
Estimated market interest rate for similar nonconvertible instrument									7.10%
Debt instrument, convertible, remaining amortization period (in Duration)				4 years 8 months 6 days
Extinguishment of Debt, Amount				$ 10,500,000			74,600,000
Repurchase price upon fundamental change as described in 2021 Notes indenture				100.00%
Debt Instrument, Face Amount				$ 1,000,000			11,500,000
Conversion Rate per $1,000 Principal Amount (in Ratio)		262.2951
Debt Instrument, Redeemable, Threshold Percentage of Stock Price Minimum				128.00%
Debt Instrument, Convertible, Threshold Percentage of Stock Price Trigger				130.00%
Debt Instrument, Convertible, Threshold Consecutive Trading Days				20
Debt Instrument, Convertible, Threshold Trading Days				30
Net receipts for capped call transactions			$ 5,000,000
Gain on conversion of convertible notes				$ (500,000)			$ (2,100,000)