Debt - Narrative (Detail)			3 Months Ended		9 Months Ended		12 Months Ended
	May 04, 2020 USD ($) day $ / shares Rate	Jun. 27, 2019 USD ($)	Sep. 30, 2020 USD ($) $ / shares Rate shares	Sep. 30, 2019 USD ($) shares	Sep. 30, 2020 USD ($) $ / shares Rate shares	Sep. 30, 2019 USD ($) shares	Dec. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Issuance of common stock, net					$ 10,761,000	$ 10,132,000
Dilutive effect of Convertible Notes (in shares) | shares			5,538,360	0	0	0
Ownership of convertible notes (as a percent)	25.00%
Proceeds from issuance of convertible debt, net of issuance costs					$ 194,466,000	$ 0
Short-term portion of term loan			$ 0		0		$ 5,000,000
Long-term portion of term loan, net			0		0		91,829,000
Debt issuance costs			565,000		565,000
Loss on extinguishment of debt			$ 0	$ 0	$ 1,400,000	$ 1,018,000	$ 1,400,000
Debt instrument, weighted average interest rates			4.91%		4.91%		4.64%
Convertible Debt
Line of Credit Facility [Line Items]
Proceeds from issuance of convertible debt, net of issuance costs	$ 96,300,000
Term Loan Facility
Line of Credit Facility [Line Items]
Debt issuance costs			$ 0		$ 0		$ 671,000
1.25% Convertible Senior Notes | Convertible Debt
Line of Credit Facility [Line Items]
Stated interest rate (as a percent) | Rate	1.25%		1.25%		1.25%
Debt instrument, face amount	$ 201,300,000
Discount on principal amount (as a percent) | Rate	97.00%
Discount on shares	$ 6,900,000
Threshold trading days | day	20
Consecutive trading days | day	30
Conversion price on applicable trading day (as a percent)	130.00%
Convertible Notes, conversion ratio | Rate	2.75198%
Convertible Notes, conversion price (in dollars per share) | $ / shares	$ 36.34		$ 36.89		$ 36.89
Convertible debt, if converted, value in excess of principal	$ 3,100,000
Redemption price of principal (as a percent)	100.00%
Interest expense, contractual coupon interest			$ 600,000		$ 1,000,000.0
Interest expense, accretion of debt discount			1,800,000		2,700,000
Interest expense, amortization of debt issuance costs			25,600		$ 44,700
Effective interest rate on Convertible Notes (as a percent)					5.50%
Carrying amount of equity component	$ 21,600,000		23,100,000		$ 23,100,000
Debt issuance costs			$ 565,000		$ 565,000		$ 0
1.25% Convertible Senior Notes | Convertible Debt | Debt Instrument, Redemption, Period One
Line of Credit Facility [Line Items]
Threshold trading days | day	20
Consecutive trading days | day	30
Conversion price on applicable trading day (as a percent)	130.00%
1.25% Convertible Senior Notes | Convertible Debt | Debt Instrument, Redemption, Period Two
Line of Credit Facility [Line Items]
Threshold trading days | day	5
Consecutive trading days | day	5
Principal amount priced to investors (as a percent) | Rate	98.00%
New Credit Agreement | Federal Funds Rate
Line of Credit Facility [Line Items]
Debt instrument variable interest rate					0.50%
New Credit Agreement | LIBOR
Line of Credit Facility [Line Items]
Debt instrument variable interest rate					1.00%
New Credit Agreement | LIBOR | Minimum
Line of Credit Facility [Line Items]
Debt instrument applicable margin					1.25%
New Credit Agreement | LIBOR | Maximum
Line of Credit Facility [Line Items]
Debt instrument applicable margin					2.25%
New Credit Agreement | Base Rate | Minimum
Line of Credit Facility [Line Items]
Debt instrument applicable margin					0.25%
New Credit Agreement | Base Rate | Maximum
Line of Credit Facility [Line Items]
Debt instrument applicable margin					1.25%
New Credit Agreement | Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity		$ 100,000,000.0
Line of credit facility, swingline sublimit		$ 10,000,000.0
New Credit Agreement | Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Commitment fee (as a percent)		0.15%
New Credit Agreement | Revolving Credit Facility | Maximum
Line of Credit Facility [Line Items]
Commitment fee (as a percent)		0.35%
New Credit Agreement | Term Loan
Line of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity		$ 100,000,000.0
Annual principal amortization, year one (as a percent)		5.00%
Annual principal amortization, year two (as a percent)		5.00%
Annual principal amortization, year three (as a percent)		7.50%
Annual principal amortization, year four (as a percent)		7.50%
Annual principal amortization, thereafter (as a percent)		10.00%
Debt instrument, percentage of net cash proceeds from sales and dispositions subject to certain reinvestment rights			100.00%		100.00%
Debt instrument, percentage of net cash proceeds from issuances or incurrence of additional debt to be used for mandatory prepayment			100.00%		100.00%
New Credit Agreement | Delayed Draw Term Loan
Line of Credit Facility [Line Items]
Line of credit facility maximum borrowing capacity		$ 50,000,000.0
Over-Allotment Option
Line of Credit Facility [Line Items]
Issuance of common stock, net	$ 194,400,000