Convertible Notes - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares	Mar. 31, 2017 USD ($)	Sep. 30, 2014 USD ($) d $ / shares	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Aggregate amount of senior notes issued	$ 125,000,000			$ 125,000,000
Debt instrument, anniversary term	7 years
Unamortized discount, gross	$ (1,078,000)			(1,155,000)
Convertible notes
Debt Instrument [Line Items]
Debt instrument, interest rate percentage			1.75%
Debt instrument, convertible, stock price trigger (in dollars per share) | $ / shares			$ 30
Debt instrument, convertible, threshold trading days | d			30
Debt instrument, convertible, ownership cap in shares of common stock (as a percentage)	9.985%
Debt instrument, convertible, initial conversion price per share (in dollars per share) | $ / shares	$ 24.80
Debt instrument, convertible, common stock conversion rate per $1,000 principal amount	0.04032
Debt instrument, convertible, conversion premium percentage	30.00%
Debt instrument, convertible, maximum increase to the initial conversion rate per $1,000 principal amount (in shares) | shares	0.01207
Default provisions, qualifying percentage of ownership (more than)	50.00%
Interest expense related to convertible notes	$ 500,000	$ 600,000
2014 Notes | Convertible notes
Debt Instrument [Line Items]
Aggregate amount of senior notes issued			$ 125,000,000	$ 125,000,000.0
Percentage of voting rights pledged as collateraltion, percentage of voting interests acquired	65.00%
Unamortized discount, gross	$ (2,100,000)