Nature of operations and summary of significant accounting policies (Income Taxes) (Detail) - USD ($) |
3 Months Ended | 12 Months Ended | ||||
|---|---|---|---|---|---|---|
Mar. 31, 2017 |
Mar. 31, 2017 |
Mar. 21, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Income Tax Disclosure [Line Items] | ||||||
| Deferred tax benefit | $ 0 | |||||
| Uncertain tax positions | $ 0 | $ 0 | ||||
| Estimated amount of cancellation of indebtedness income | $ 61,000,000 | |||||
| Predecessor | ||||||
| Income Tax Disclosure [Line Items] | ||||||
| Deferred tax benefit | $ 0 | $ 0 | $ (177,393,000) | $ 123,891,000 | ||
| Uncertain tax positions | 0 | 0 | ||||
| Income tax penalties and interest accrued | $ 0 | $ 0 | ||||