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Comprehensive Income - Schedule of Changes in Balances of Each Component of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended | 9 Months Ended |
--- | --- | --- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018 | Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss), Restated |  |  |  |  |  |  | $ (55,139)
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets |  |  |  |  |  |  | (2,900)
Changes In Accumulated Other Comprehensive Income [Roll Forward] |  |  |  |  |  |  |
Beginning Balance | $ 22,542 | $ 99,476 | $ (48,715) | $ (52,239) | $ (52,239) |  |
Other comprehensive income before reclassifications | (32,565) | 6,280 | (121,192) | (152,087) |  |  |
Amounts reclassified from accumulated other comprehensive income | (36,019) | (47,342) | (53,389) | (51,094) |  |  |
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent | (3,454) | (53,622) | 67,803 | 100,993 |  |  |
Ending Balance | 19,088 | 45,854 | 19,088 | 45,854 |  |  |
Income Tax Expense (Benefit) | 28,322 | 1,995 | 30,313 | 4,600 | 30,313 | $ 4,600 |
Unrealized Gains (Losses) on Available-for-Sale Securities [Member] |  |  |  |  |  |  |
Changes In Accumulated Other Comprehensive Income [Roll Forward] |  |  |  |  |  |  |
Beginning Balance | 142,066 | 153,059 | 85,903 | 30,755 | 30,755 |  |
Other comprehensive income before reclassifications | (51,098) | (46,709) | (124,465) | (173,576) |  |  |
Amounts reclassified from accumulated other comprehensive income | (35,860) | (46,134) | (53,064) | (50,697) |  |  |
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent | 15,238 | 575 | 71,401 | 122,879 |  |  |
Ending Balance | 157,304 | 153,634 | 157,304 | 153,634 |  |  |
Accumulated Translation Adjustment [Member] |  |  |  |  |  |  |
Changes In Accumulated Other Comprehensive Income [Roll Forward] |  |  |  |  |  |  |
Beginning Balance | (126,956) | (61,578) | (141,527) | (93,634) | (93,634) |  |
Other comprehensive income before reclassifications | 18,533 | 52,989 | 3,962 | 20,933 |  |  |
Amounts reclassified from accumulated other comprehensive income | 0 | 0 | 0 | 0 |  |  |
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent | (18,533) | (52,989) | (3,962) | (20,933) |  |  |
Ending Balance | (145,489) | (114,567) | (145,489) | (114,567) |  |  |
Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member] |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets |  |  |  |  |  |  | $ (2,900)
Changes In Accumulated Other Comprehensive Income [Roll Forward] |  |  |  |  |  |  |
Beginning Balance | (1,809) | (1,786) | (1,965) | (2,900) | (2,900) |  |
Other comprehensive income before reclassifications | 0 | 0 | 0 | 0 |  |  |
Amounts reclassified from accumulated other comprehensive income | 163 | (906) | 319 | 208 |  |  |
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent | 163 | (906) | 319 | 208 |  |  |
Ending Balance | (1,646) | (2,692) | (1,646) | (2,692) |  |  |
Other Postretirement Benefits Plan [Member] |  |  |  |  |  |  |
Changes In Accumulated Other Comprehensive Income [Roll Forward] |  |  |  |  |  |  |
Beginning Balance | 9,241 | 9,781 | 8,874 | 10,640 | $ 10,640 |  |
Other comprehensive income before reclassifications | 0 | 0 | (689) | 556 |  |  |
Amounts reclassified from accumulated other comprehensive income | (322) | (302) | (644) | (605) |  |  |
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent | (322) | (302) | 45 | (1,161) |  |  |
Ending Balance | 8,919 | 9,479 | 8,919 | 9,479 |  |  |
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Available-for-Sale Securities [Member] |  |  |  |  |  |  |
Changes In Accumulated Other Comprehensive Income [Roll Forward] |  |  |  |  |  |  |
Income Tax Expense (Benefit) | 5,023 | 1,122 | 4,512 | (586) |  |  |
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Gain (Loss), Financial Liability, Fair Value Option, Attributable to Parent [Member] |  |  |  |  |  |  |
Changes In Accumulated Other Comprehensive Income [Roll Forward] |  |  |  |  |  |  |
Income Tax Expense (Benefit) |  |  | (65) |  |  |  |
Reclassification out of Accumulated Other Comprehensive Income [Member] | Other Postretirement Benefits Plan [Member] |  |  |  |  |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax | (241) | (241) | (482) | (482) |  |  |
Changes In Accumulated Other Comprehensive Income [Roll Forward] |  |  |  |  |  |  |
Amounts reclassified from accumulated other comprehensive income | (322) | (302) | (644) | (605) |  |  |
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax | 81 | 61 | 162 | 123 |  |  |
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest | (322) | (302) | (644) | (605) |  |  |
Income Tax Expense (Benefit) | $ 0 | $ 0 | $ 0 | $ 0 |  |  |

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