Equity Incentive Compensation Plans and Other Long-term Incentive Programs - Additional Information (Detail) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 shares	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2018 shares	Dec. 31, 2018 USD ($) integer $ / shares
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Common Stock, Par or Stated Value Per Share (in dollars per share) | $ / shares	$ 0.001		$ 0.001		$ 0.001
Unrecognized compensation cost | $	$ 10.1		$ 10.1
Weighted-average period (years)			1 year 10 months 24 days
Nonvested Equity Shares
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Award vesting period			3 years
Total shares granted (in shares)	6,000	221,025	1,841,700	1,017,448
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)	30,031	15,724	1,329,630	667,932
Nonvested Equity Common Stock Units
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Award vesting period			1 year
Cash-Based Award
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Award vesting period			3 years
Nonvested Performance Cash Units
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred Compensation Cash-based Arrangements, Liability, Classified, Noncurrent | $	$ 1.4		$ 1.4		$ 0.3
Total shares granted (in shares)	0	49,833	2,026,521	846,256
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares)			0	286,652
Two Thousand And Fifteen Performance Program [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Percent of Performance Based Shares Vested					104.10%
Two Thousand And Sixteen Performance Program [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Percentage Of Original Award Converted To Nonvested Common Stock Award					89.00%
Number Of Units Not Converted To Nonvested Common Stock | integer					65,173
Two Thousand Eighteen Performance Program [Domain]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Performance Goal Measurement Period			3 years
Closing Share Price, December 31, 2018 | $ / shares	$ 2.49		$ 2.49
Absolute Performance Is Less Than 50%			50.00%
Payout Is Zero If Absolute Performance Is Less Than 50%			0.00%
Absolute Performance Is 50%			50.00%
Payout Is 50% If Absolute Performance Is 50%			50.00%
Absolute Performance Is 100%			100.00%
Payout Is 100% If Absolute Performance Is 100%			100.00%
Relative TSR Is Less Than 30%			30.00%
Payout Is Zero If Relative TSR Is Less Than 30%			0.00%
Relative TSR Is 30% Or Greater			30.00%
Payout Is Equal To Percentile Rank, Up To 100%, If Relative TSR Is Greater Than 30%			100.00%
Two Thousand Eighteen Performance Program [Domain] | Absolute Performance and Relative TSR | Maximum
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Award vesting rights, percentage			200.00%