Fair Value Measurement - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 05, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Expected volatility rate				60.00%		40.00%
Risk free interest rate				1.10%		0.60%
Expected probability of qualified acquisition				50.00%		90.00%
Qualified acquisition, expected term				6 months		6 months
Net income attributable to common and participating stockholders		$ 33,911	$ (21,145)	$ 21,376	$ 47,814
Increase decrease in estimated net income (loss) if percentage of closing stock price ten percent lower				39,100
Increase decrease in estimated net income (loss) if percentage of closing stock price ten percent higher				3,800
Volatility Assumption [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Increase decrease in estimated net income (loss) if percentage of closing stock price ten percent lower				24,400
Increase decrease in estimated net income (loss) if percentage of closing stock price ten percent higher				18,100
Transaction Occurring Assumption [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Increase decrease in estimated net income (loss) if percentage of closing stock price ten percent lower				1,000
Increase decrease in estimated net income (loss) if percentage of closing stock price ten percent higher				$ 43,800
Maximum [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of closing stock price				10.00%
Estimated net income				$ 17,700
Maximum [Member] | Volatility Assumption [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of closing stock price				10.00%
Estimated net income				$ 3,000
Maximum [Member] | Transaction Occurring Assumption [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of closing stock price				10.00%
Estimated net income				$ 22,400
Minimum [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of closing stock price				10.00%
Estimated net income				$ 17,600
Minimum [Member] | Volatility Assumption [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of closing stock price				10.00%
Estimated net income				$ 3,300
Minimum [Member] | Transaction Occurring Assumption [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Percentage of closing stock price				10.00%
Estimated net income				$ 22,400
Redeemable Convertible Series B Preferred Stock [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Capital	$ 600,000
Redeemable Convertible preferred stock, shares issued	600,000	600,000		600,000		600,000
Preferred stock liquidation preference per share	$ 1,000
Preferred stock dividend rate calculated on interest rate	3.00%
Conversion ceiling price of common stock		$ 2.25		$ 2.25
Conversion floor price of common stock		1.75		1.75
Redeemable Convertible Series B Preferred Stock [Member] | Maximum [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Conversion ceiling price of common stock		$ 2.25		$ 2.25