| **Accumulated other comprehensive loss - Summary of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands** | 3 Months Ended | 6 Months Ended |
|------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                   |           |           |   |   |   |   |
| Accumulated other comprehensive income (loss), beginning balance                                                             |           | $ 2,159,130    |   |   | $ 2,159,130 |   |
| Amortization of prior service costs and net    actuarial losses, net of tax of ($1,850)                            | $ 2,778        |           | $ 3,804 |   | 5,838 | $ 6,801 |
| Foreign currency translation adjustments                                                                                     | (46,901)       | (13,358)       | (6,943) | $ 28,433 | (60,259) | 21,490 |
| Pension settlement, net of tax of ($9,573)                                                                                   | 32,047         |           | 4,581 |   | 32,047 | $ 4,581 |
| Accumulated other comprehensive loss, ending balance                                                                         | 2,190,616      |           |   |   | 2,190,616 |   |
| Amortization of prior service costs and net actuarial losses, tax                                                            |           |           |   |   | 1,850 |   |
| Pension settlement tax                                                                                                       |           |           |   |   | 9,573 |   |
| Accumulated Other Comprehensive Income (Loss)                                                                                |           |           |   |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                   |           |           |   |   |   |   |
| Accumulated other comprehensive income (loss), beginning balance                                                             |           | (175,835)      |   |   | (175,835) |   |
| Foreign currency translation adjustments                                                                                     | (46,901)       | (13,358)       | $ (6,943) | $ 28,433 |   |   |
| Pension settlement, net of tax of ($9,573)                                                                                   | 32,047         |           |   |   |   |   |
| Accumulated other comprehensive loss, ending balance                                                                         | (198,209)      |           |   |   | (198,209) |   |
| Cumulative translation adjustments                                                                                           |           |           |   |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                   |           |           |   |   |   |   |
| Accumulated other comprehensive income (loss), beginning balance                                                             |           | (33,389)       |   |   | (33,389) |   |
| Amortization of prior service costs and net    actuarial losses, net of tax of ($1,850)                            |           |           |   |   | 0 |   |
| Foreign currency translation adjustments                                                                                     |           |           |   |   | (60,259) |   |
| Pension settlement, net of tax of ($9,573)                                                                                   |           |           |   |   | 0 |   |
| Accumulated other comprehensive loss, ending balance                                                                         | (93,648)       |           |   |   | (93,648) |   |
| Pension and postretirement  benefit plan adjustments                                                               |           |           |   |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                   |           |           |   |   |   |   |
| Accumulated other comprehensive income (loss), beginning balance                                                             |           | $ (142,446)    |   |   | (142,446) |   |
| Amortization of prior service costs and net    actuarial losses, net of tax of ($1,850)                            |           |           |   |   | 5,838 |   |
| Foreign currency translation adjustments                                                                                     |           |           |   |   | 0 |   |
| Pension settlement, net of tax of ($9,573)                                                                                   |           |           |   |   | 32,047 |   |
| Accumulated other comprehensive loss, ending balance                                                                         | $ (104,561)    |           |   |   | $ (104,561) |   |

| X                                                                                                                                                                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.
+ References
No definition available.
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| - Definition
Amount, after tax, of cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of tax expense (benefit) for increase (decrease) to other comprehensive income from settlement and curtailment gain (loss) of defined benefit plan.
+ References
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| - Definition
Amount, after tax, of increase (decrease) to other comprehensive income from settlement and curtailment gain (loss) of defined benefit plan.
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| - Definition
Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.
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| - Definition
Amount, after reclassification adjustment, of tax (expense) benefit for (increase) decrease in accumulated other comprehensive income of defined benefit plan.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.
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