Equity Incentive Compensation Plans and Other Long-term Incentive Programs - Stock Options and Nonvested Equity Shares, Equity Awards Granted (Detail)		3 Months Ended		9 Months Ended
	Mar. 19, 2018 integer	Sep. 30, 2019 $ / shares shares	Sep. 30, 2018 $ / shares shares	Sep. 30, 2019 $ / shares shares	Sep. 30, 2018 $ / shares shares
Nonvested Equity Shares
Units
Beginning balance (in shares)		3,406,134	2,858,278	2,912,166	1,394,868
Granted (in shares)		6,000	123,094	1,847,700	1,140,542
Modified (in shares)				0	1,146,305
Vested (in shares)		(356,009)	(25,432)	(1,685,639)	(693,364)
Forfeited or expired (in shares)		(73,094)	(38,292)	(91,196)	(70,703)
Ending balance (in shares)		2,983,031	2,917,648	2,983,031	2,917,648
Weighted Average Grant Date Fair Value
Beginning balance (in dollars per share) | $ / shares		$ 3.88	$ 5.28	$ 5.27	$ 7.00
Granted (in dollars per share) | $ / shares		1.25	6.79	2.64	5.60
Modified (in dollars per share) | $ / shares				0	4.84
Vested (in dollars per share) | $ / shares		4.19	7.16	4.99	8.24
Forfeited or expired (in dollars per share) | $ / shares		4.80	5.34	4.83	5.98
Ending balance (in dollars per share) | $ / shares		$ 3.82	$ 5.33	$ 3.82	$ 5.33
Nonvested Performance Cash Units
Units
Beginning balance (in shares)		2,868,634	846,256	909,585	1,548,083
Granted (in shares)		0	89,037	2,026,521	935,293
Performance goal adjustment (in shares)				0	11,289
Modified (in shares)				0	1,211,478
Vested (in shares)				0	(286,652)
Forfeited or expired (in shares)		(292,572)	(16,232)	(360,044)	(77,474)
Ending balance (in shares)		2,576,062	919,061	2,576,062	919,061
Weighted Average Grant Date Fair Value
Ending balance (in dollars per share) | $ / shares		$ 1.59	$ 4.88	$ 1.59	$ 4.88
Director
Units
Beginning balance (in shares)		796,103	302,417	311,237	272,559
Granted (in shares)		0	18,695	643,084	180,778
Vested (in shares)		0	(18,695)	(158,218)	(150,920)
Ending balance (in shares)		796,103	302,417	796,103	302,417
Weighted Average Grant Date Fair Value
Beginning balance (in dollars per share) | $ / shares		$ 3.27	$ 7.37	$ 7.26	$ 6.37
Granted (in dollars per share) | $ / shares		0	4.88	1.88	6.63
Vested (in dollars per share) | $ / shares		0	4.88	5.44	4.66
Ending balance (in dollars per share) | $ / shares		$ 3.27	$ 7.37	$ 3.27	$ 7.37
2015 Program
Weighted Average Grant Date Fair Value
Percent of performance based shares vested					104.10%
2016 Program
Weighted Average Grant Date Fair Value
Percentage of original award converted to nonvested common stock award	89.00%
Number of units not converted to nonvested common stock (in shares) | integer	65,173