Net Income Per Share - Additional Information (Detail) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended		18 Months Ended
	Dec. 31, 2019 $ / shares shares	Dec. 31, 2017 shares	Dec. 31, 2016 shares	Dec. 31, 2016 USD ($) $ / shares shares	Mar. 31, 2019 USD ($)	Dec. 31, 2018 $ / 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	45,555,400					45,336,278
Class of Warrant or Right, Outstanding	4,877,783
Number of new common stock issued	45,571,743					45,365,170
Par value of common stock issued | $ / shares	$ 0.01					$ 0.01					$ 0.01
Exercise price of common stock | $ / shares										$ 16.67
Warrant exercised	0	194	0
Stock Issued During Period, Shares, New Issues	0	194	0
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
AMPS Exchange Total Warrants Issued							824,307
AMPS Exchange Total Warrants Issued Cost Per Share | $ / shares							$ 9.72