Debt - Additional Information (Detail) $ / shares in Units, shares in Thousands, $ in Thousands		1 Months Ended	3 Months Ended					6 Months Ended	9 Months Ended
	Jun. 14, 2019 USD ($) d $ / shares	Dec. 31, 2018 USD ($)	Sep. 30, 2020 USD ($) $ / shares shares	Mar. 31, 2020	Dec. 31, 2019 USD ($)	Sep. 30, 2019 shares	Jun. 30, 2019	Dec. 31, 2019 USD ($)	Sep. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2019 USD ($) shares	Jul. 01, 2019 USD ($)
Line Of Credit Facility [Line Items]
Aggregate principal amount			$ 690,000		$ 690,000			$ 690,000	$ 690,000
Proceeds from the issuance of notes										$ 672,152
Debt instrument carrying amount of equity component conversion option			$ 114,938		$ 114,938			$ 114,938	114,938
Transaction costs attributable to the liability component									14,800
Transaction costs attributable to the equity component									$ 3,100
Anti-dilutive securities underlying conversion option | shares			109,570			5,037			83,938	4,120
Bank of America, N.A. [Member] | Credit Facility [Member]
Line Of Credit Facility [Line Items]
Credit facility expiration period		3 years
Intial aggregate principal borrowing capacity amount		$ 200,000
Debt instrument interest rate, description									At the Company’s option, revolving loans accrue interest at a per annum rate based on either (i) the base rate plus a margin ranging from 0.50% to 1.00%, determined based on the Company’s consolidated leverage ratio for the four most recent fiscal quarters (the “Consolidated Leverage Ratio”) or (ii) the LIBOR rate (for interest periods of one, two, three or six months) plus a margin ranging from 1.50% to 2.00%, determined based on the Company’s Consolidated Leverage Ratio (“LIBOR Loan”).  The base rate is defined as the highest of (i) the federal funds rate, plus 0.50%, (ii) Bank of America, N.A.’s prime rate and (iii) the LIBOR rate for a one-month interest period plus 1.00%.
Debt instrument commitment fee, description									The Company is also obligated to pay an ongoing commitment fee on undrawn amounts at a rate ranging from 0.25% to 0.35%, determined based on the Company’s Consolidated Leverage Ratio.
Line of credit facility amount outstanding			$ 0						$ 0
Debt capitalized, amortize period			3 years						3 years
Bank of America, N.A. [Member] | Credit Facility [Member] | LIBOR Rate [Member]
Line Of Credit Facility [Line Items]
Debt instrument interest rate									1.00%
Bank of America, N.A. [Member] | Credit Facility [Member] | Federal Funds Rate [Member]
Line Of Credit Facility [Line Items]
Debt instrument interest rate									0.50%
Bank of America, N.A. [Member] | Sale Agreement [Member] | Credit Facility [Member]
Line Of Credit Facility [Line Items]
Credit facility remaining borrowing capacity											$ 150,000
Minimum [Member] | Bank of America, N.A. [Member] | Credit Facility [Member]
Line Of Credit Facility [Line Items]
Payment for commitment fee, percentage									0.25%
Minimum [Member] | Bank of America, N.A. [Member] | Credit Facility [Member] | Base Rate [Member]
Line Of Credit Facility [Line Items]
Debt instrument interest rate				0.50%	0.50%	0.50%	0.50%
Minimum [Member] | Bank of America, N.A. [Member] | Credit Facility [Member] | LIBOR Rate [Member]
Line Of Credit Facility [Line Items]
Debt instrument interest rate								1.50%
Maximum [Member] | Bank of America, N.A. [Member] | Credit Facility [Member]
Line Of Credit Facility [Line Items]
Payment for commitment fee, percentage									0.35%
Maximum [Member] | Bank of America, N.A. [Member] | Credit Facility [Member] | Base Rate [Member]
Line Of Credit Facility [Line Items]
Debt instrument interest rate				1.00%	1.00%	1.00%	1.00%
Maximum [Member] | Bank of America, N.A. [Member] | Credit Facility [Member] | LIBOR Rate [Member]
Line Of Credit Facility [Line Items]
Debt instrument interest rate								2.00%
Capped Call Transactions [Member]
Line Of Credit Facility [Line Items]
Initial strike price | $ / shares			8.31						8.31
Initial cap price | $ / shares			12.54						12.54
Cost incurred for Capped Calls									$ 73,800
Class A Common stock [Member] | Capped Call Transactions [Member]
Line Of Credit Facility [Line Items]
Capped calls economic dilutive potential common stock shares | shares									83,100
Class A Common stock [Member] | Conversion Senior Notes and Capped Call Transactions [Member]
Line Of Credit Facility [Line Items]
Anti-dilutive securities underlying conversion option | shares									83,100
Class A Common stock [Member] | Conversion Senior Notes and Capped Call Transactions [Member] | Minimum [Member]
Line Of Credit Facility [Line Items]
Initial strike price | $ / shares			8.31						8.31
Convertible Senior Notes Due 2024 [Member]
Line Of Credit Facility [Line Items]
Aggregate principal amount	$ 690,000
Debt instrument, interest rate	0.25%
Additional aggregate principal amount	$ 90,000
Proceeds from the issuance of notes	$ 672,200
Debt instrument maturity date	Jun. 01, 2024
Debt instrument payment terms									The Notes mature on June 1, 2024 unless earlier converted, redeemed or repurchased in accordance with their term prior to the maturity date. Interest is payable semiannually in arrears on June 1 and December 1 of each year, beginning on December 1, 2019
Debt repurchase price percentage	100.00%
Debt instrument initial carrying amount	$ 572,000
Interest rate used to calculate the present value of the cash flows	4.10%
Debt instrument carrying amount of equity component conversion option	$ 118,000
Contractual term	5 years
Debt instrument, if-converted value									$ 757,500
Debt Instrument, if-converted value in excess of principal amount									67,500
Convertible Senior Notes Due 2024 [Member] | Fair Value, Inputs, Level 2 [Member]
Line Of Credit Facility [Line Items]
Debt instrument estimated fair value			$ 874,400						$ 874,400
Convertible Senior Notes Due 2024 [Member] | Class A Common stock [Member]
Line Of Credit Facility [Line Items]
Initial conversion rate of common stock per $1,000 principal amount	120.3695
Initial conversion price per share of common stock | $ / shares	$ 8.31
Debt instrument threshold trading days to trigger conversion feature | d	20
Debt instrument threshold consecutive trading days to trigger conversion feature | d	30
Debt instrument, minimum percentage of common stock price to determine eligibility of conversion	130.00%
Consecutive business trading period when trading price meets required criteria as a condition for conversion of debt	5 days
Trading price percentage of product of last reported sales price as a condition for conversion of debt	98.00%
Debt instrument redemption start date	Jun. 05, 2022
Debt instrument redemption price percentage	100.00%
Debt instrument, closing price of common stock | $ / shares									$ 9.12