Stock-Based Compensation Plans and Arrangements - Restricted Stock and Performance Stock Unit Activity (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Weighted Average Grant Date Fair Value
Unrecognized compensation cost	$ 14.8
Weighted average period for total unrecognized compensation cost	1 year 4 months 15 days
Restricted Stock
Number of Shares
Non-vested at December 31, 2015 (in shares)	86,174
Granted (in shares)	120,879
Vested and converted to common stock (in shares)	(86,174)
Canceled (in shares)	0
Non-vested at December 31, 2016 (in shares)	120,879	86,174
Weighted Average Grant Date Fair Value
Non-vested at December 31, 2015 (in dollars per share)	$ 8.94
Granted (in dollars per share)	6.37
Vested (in dollars per share)	8.94
Canceled (in dollars per share)	0.00
Non-vested at December 31, 2016 (in dollars per share)	$ 6.37	$ 8.94
Fair value of shares vested	$ 0.8	$ 0.5	$ 0.4
Unrecognized compensation cost	$ 0.4
Weighted average period for total unrecognized compensation cost	6 months
Restricted Stock Units And Performance Stock Units
Number of Shares
Non-vested at December 31, 2015 (in shares)	5,840,388
Granted (in shares)	4,508,818
Vested and converted to common stock (in shares)	(2,798,828)
Canceled (in shares)	(63,768)
Non-vested at December 31, 2016 (in shares)	7,486,610	5,840,388
Weighted Average Grant Date Fair Value
Non-vested at December 31, 2015 (in dollars per share)	$ 8.52
Granted (in dollars per share)	5.95
Vested (in dollars per share)	7.92
Canceled (in dollars per share)	7.02
Non-vested at December 31, 2016 (in dollars per share)	$ 7.21	$ 8.52
Fair value of restricted stock units that vested and converted to common stock	$ 22.2	$ 18.9	$ 12.6
Unrecognized compensation cost	$ 14.3
Weighted average period for total unrecognized compensation cost	1 year 4 months 24 days