Mandatorily Redeemable Preferred Stock - Additional Information (Detail) - Mandatorily Redeemable Preferred Stock	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($) vote / shares $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares
Financial Instruments Subject to Mandatory Redemption by Settlement Terms [Line Items]
Preferred stock, authorized (shares)	350,000,000.0	350,000,000
Preferred stock, par value (dollars per share) | $ / shares	$ 0.01	$ 0.01
Preferred stock, issued (shares)	7,133	21,202
Preferred stock, outstanding (shares)	7,133	21,202
Preferred stock, redemption rate (percent)	8.00%	8.00%
Number of votes per share | vote / shares	1
Preferred stock, redemption value | $	$ 1,000	$ 1,000
Estimated fair value | $	$ 7,100,000	$ 21,300,000