Debt - Additional Information (Detail) shares in Thousands					1 Months Ended	3 Months Ended					6 Months Ended
	Jun. 19, 2019 USD ($)	Jun. 14, 2019 USD ($) d $ / shares	Mar. 28, 2019	Dec. 28, 2018 USD ($)	Dec. 31, 2018 USD ($)	Jun. 30, 2019 USD ($) $ / shares shares	Mar. 31, 2019	Dec. 31, 2018 USD ($)	Sep. 30, 2018	Jun. 30, 2018 shares	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 shares	Jul. 01, 2019 USD ($)
Line Of Credit Facility [Line Items]
Aggregate principal amount						$ 690,000,000					$ 690,000,000
Proceeds from the issuance of notes											672,682,000
Debt instrument carrying amount of equity component conversion option						$ 114,974,000					114,974,000
Transaction costs attributable to the liability component											14,600,000
Transaction costs attributable to the equity component											$ 3,000,000.0
Anti-dilutive securities underlying conversion option | shares						86,242				91,814	86,653	12,457
Bank of America, N.A. [Member] | Credit Facility [Member]
Line Of Credit Facility [Line Items]
Credit facility expiration period			3 months	3 months	3 years
Aggregate principal borrowing capacity amount					$ 200,000,000.0			$ 200,000,000.0
Credit facility remaining borrowing capacity					$ 150,000,000.0			$ 150,000,000.0
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.
Borrowings under credit facility				$ 100,000,000.0
Debt instrument effective interest rate			4.10%	4.31%
Repayment of credit facility	$ 100,000,000.0
Available borrowing capacity under credit facility						$ 200,000,000.0					$ 200,000,000.0
Debt capitalized, amortize period						3 years					3 years
Bank of America, N.A. [Member] | Credit Facility [Member] | Sale Agreement [Member] | Subsequent Event [Member]
Line Of Credit Facility [Line Items]
Aggregate principal borrowing capacity amount													$ 150,000,000.0
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%
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											$ 73,800,000
Common Class A [Member] | Capped Call Transactions [Member]
Line Of Credit Facility [Line Items]
Capped calls economic dilutive potential common stock shares | shares											83,100
Common Class A [Member] | Conversion Senior Notes and Capped Call Transactions [Member]
Line Of Credit Facility [Line Items]
Anti-dilutive securities underlying conversion option | shares						83,100					83,100
Common Class A [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		$ 690,000,000.0
Debt instrument, interest rate		0.25%
Additional aggregate principal amount		$ 90,000,000.0
Proceeds from the issuance of notes		$ 672,400,000
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		$ 572,000,000.0
Interest rate used to calculate the present value of the cash flows		4.10%
Debt instrument carrying amount of equity component conversion option		$ 118,000,000.0
Contractual term		5 years
Convertible Senior Notes Due 2024 [Member] | Fair Value, Inputs, Level 2 [Member]
Line Of Credit Facility [Line Items]
Debt instrument estimated fair value						$ 671,300,000					$ 671,300,000
Convertible Senior Notes Due 2024 [Member] | Common Class A [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%