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Employee Benefit Plans - Postretirement Healthcare Plan (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Defined Benefit Plan Disclosure |  |  |  |
Amortization of gain, weighted average remaining service period (in years) |  | 4 years |  |
Stockholders’ equity | $ 1,693,900 | $ 1,427,600 | $ 982,600 | $ 950,500
Defined Benefit Plan, Expected Future Benefit Payment [Abstract] |  |  |  |
Defined Benefit Plan, Amortization of Transition Asset (Obligation) | $ 700 |  |  |
Postretirement Healthcare Plan |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Minimum age requirement | 55 years |  |  |
Requisite service period | 15 years |  |  |
Accumulated other comprehensive income (loss), before tax, related to the Plan | $ 1,200 |  |  |
Reduction in accumulated post-retirement benefit obligation due to curtailment |  |  | 2,800 |
Reduction in net periodic benefit cost due to curtailment | (2,800) | (300) |  |
Unfunded benefit obligation | (500) | (700) |  |
Net periodic benefit cost | 800 | $ 400 | $ 200 |
Defined Benefit Plan, Expected Future Benefit Payment [Abstract] |  |  |  |
2019 | 120 |  |  |
2020 | 90 |  |  |
2021 | 60 |  |  |
2022 | 50 |  |  |
2023 through 2027 | 100 |  |  |
Estimated amount amortized from accumulated other comprehensive loss into net periodic benefit costs | $ 140 |  |  |
Minimum |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Assumptions used calculating net periodic benefit cost, discount rate | 3.60% | 2.40% |  |
Maximum |  |  |  |
Defined Benefit Plan Disclosure |  |  |  |
Assumptions used calculating net periodic benefit cost, discount rate | 6.00% | 6.00% |  |

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- Definition Defined Benefit Plan with Individual, Minimum Age Requirement + References No definition available. + Details
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- Definition Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669646-108580 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669686-108580 + Details
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