Net Income Per Share - Additional Information (Detail) $ / shares in Units, $ in Millions	12 Months Ended			66 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 $ / shares shares	Dec. 31, 2018 shares	Dec. 31, 2020 USD ($) $ / shares shares	Aug. 03, 2018 $ / shares	Nov. 02, 2016 USD ($)	Jun. 30, 2015 USD ($)	May 01, 2013 $ / shares	Apr. 30, 2013 $ / shares
Schedule Of Earnings Per Share [Line Items]
Common Stock, Shares, Outstanding	45,809,139			45,809,139
Class of Warrant or Right, Outstanding	4,877,749			4,877,749
Number of new common stock issued	45,865,081	45,571,743		45,865,081
Common Stock, Par or Stated Value Per Share | $ / shares	$ 0.01	$ 0.01		$ 0.01					$ 0.01
Exercise price of common stock | $ / shares								$ 16.67
Warrant exercised	34	0	194
Stock Issued During Period, Shares, New Issues	8	0	194
First Warrant Buyback Authorization Dollars | $							$ 10
Payments for Repurchase of Warrants | $				$ 8
Warrants Repurchased Average Cost per Warrant | $ / shares				$ 8.21
SecondWarrantBuyBackAuthorizedDollars | $						$ 10
Warrants Purchased Shares				985,331
RemainingWarrantBuyBackAuthorizedDollars | $	$ 12			$ 12
AMPS Exchange Total Warrants Issued					824,307
AMPS Exchange Total Warrants Issued Cost Per Share | $ / shares					$ 9.72