Employee Benefit Plans: Employee Benefit Plans Fair Value Measurements (Details) - USD ($) $ in Thousands | 12 Months Ended | | |
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 |
Hedge Funds | Minimum | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Percentage Of Monthly Redemption | 20.00% | | |
Hedge Funds | Maximum | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Percentage Of Quarterly Redemption | 100.00% | | |
Pension Plans, Defined Benefit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | $ 390,796 | $ 416,343 | $ 364,695 |
Other Postretirement Benefit Plans, Defined Benefit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 8,162 | 8,621 | $ 8,470 |
Fair Value, Measurements, Recurring | Pension Plans, Defined Benefit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 390,796 | 416,343 | |
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments | 358,462 | 377,017 | |
Alternative Investment, Fair Value Disclosure | 32,334 | 39,326 | |
Fair Value, Measurements, Recurring | Pension Plans, Defined Benefit | Fixed Income Funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 1,867 | 1,280 | |
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments | 1,867 | 1,280 | |
Alternative Investment, Fair Value Disclosure | 0 | 0 | |
Fair Value, Measurements, Recurring | Pension Plans, Defined Benefit | Common Collective Trust - Cash and Cash Equivalents | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 9,923 | 2,184 | |
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments | 9,923 | 2,184 | |
Alternative Investment, Fair Value Disclosure | 0 | 0 | |
Fair Value, Measurements, Recurring | Pension Plans, Defined Benefit | Common Collective Trust - Equity | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 67,457 | 109,496 | |
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments | 67,457 | 109,496 | |
Alternative Investment, Fair Value Disclosure | 0 | 0 | |
Fair Value, Measurements, Recurring | Pension Plans, Defined Benefit | Common Collective Trust - Fixed Income | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 279,148 | 262,329 | |
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments | 279,148 | 262,329 | |
Alternative Investment, Fair Value Disclosure | 0 | 0 | |
Fair Value, Measurements, Recurring | Pension Plans, Defined Benefit | Common Collective Trust - Real Estate | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 13,618 | 17,429 | |
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments | 67 | 1,728 | |
Alternative Investment, Fair Value Disclosure | 13,551 | 15,701 | |
Fair Value, Measurements, Recurring | Pension Plans, Defined Benefit | Hedge Funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 18,783 | 23,625 | |
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments | 0 | 0 | |
Alternative Investment, Fair Value Disclosure | 18,783 | 23,625 | |
Fair Value, Measurements, Recurring | Other Postretirement Benefit Plans, Defined Benefit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 8,162 | 8,621 | |
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments | 8,162 | 8,621 | |
Alternative Investment, Fair Value Disclosure | 0 | 0 | |
Fair Value, Measurements, Recurring | Other Postretirement Benefit Plans, Defined Benefit | Cash and Cash Equivalents | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 4,873 | 4,671 | |
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments | 4,873 | 4,671 | |
Alternative Investment, Fair Value Disclosure | 0 | 0 | |
Fair Value, Measurements, Recurring | Other Postretirement Benefit Plans, Defined Benefit | Equity Securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 1,005 | 1,374 | |
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments | 1,005 | 1,374 | |
Alternative Investment, Fair Value Disclosure | 0 | 0 | |
Fair Value, Measurements, Recurring | Other Postretirement Benefit Plans, Defined Benefit | Intermediate - Term Bond | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 2,284 | 2,576 | |
Defined Benefit Plan, Fair Value of Plan Assets, Excluding Net Asset Value investments | 2,284 | 2,576 | |
Alternative Investment, Fair Value Disclosure | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Pension Plans, Defined Benefit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Pension Plans, Defined Benefit | Fixed Income Funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Pension Plans, Defined Benefit | Common Collective Trust - Cash and Cash Equivalents | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Pension Plans, Defined Benefit | Common Collective Trust - Equity | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Pension Plans, Defined Benefit | Common Collective Trust - Fixed Income | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Pension Plans, Defined Benefit | Common Collective Trust - Real Estate | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Pension Plans, Defined Benefit | Hedge Funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Other Postretirement Benefit Plans, Defined Benefit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 5,878 | 6,045 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Other Postretirement Benefit Plans, Defined Benefit | Cash and Cash Equivalents | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 4,873 | 4,671 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Other Postretirement Benefit Plans, Defined Benefit | Equity Securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 1,005 | 1,374 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Other Postretirement Benefit Plans, Defined Benefit | Intermediate - Term Bond | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Pension Plans, Defined Benefit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 358,462 | 377,017 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Pension Plans, Defined Benefit | Fixed Income Funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 1,867 | 1,280 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Pension Plans, Defined Benefit | Common Collective Trust - Cash and Cash Equivalents | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 9,923 | 2,184 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Pension Plans, Defined Benefit | Common Collective Trust - Equity | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 67,457 | 109,496 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Pension Plans, Defined Benefit | Common Collective Trust - Fixed Income | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 279,148 | 262,329 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Pension Plans, Defined Benefit | Common Collective Trust - Real Estate | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 67 | 1,728 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Pension Plans, Defined Benefit | Hedge Funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Postretirement Benefit Plans, Defined Benefit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 2,284 | 2,576 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Postretirement Benefit Plans, Defined Benefit | Cash and Cash Equivalents | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Postretirement Benefit Plans, Defined Benefit | Equity Securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Postretirement Benefit Plans, Defined Benefit | Intermediate - Term Bond | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 2,284 | 2,576 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Pension Plans, Defined Benefit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Pension Plans, Defined Benefit | Fixed Income Funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Pension Plans, Defined Benefit | Common Collective Trust - Cash and Cash Equivalents | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Pension Plans, Defined Benefit | Common Collective Trust - Equity | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Pension Plans, Defined Benefit | Common Collective Trust - Fixed Income | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Pension Plans, Defined Benefit | Common Collective Trust - Real Estate | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Pension Plans, Defined Benefit | Hedge Funds | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Other Postretirement Benefit Plans, Defined Benefit | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Other Postretirement Benefit Plans, Defined Benefit | Cash and Cash Equivalents | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Other Postretirement Benefit Plans, Defined Benefit | Equity Securities | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | 0 | 0 | |
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Other Postretirement Benefit Plans, Defined Benefit | Intermediate - Term Bond | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Defined Benefit Plan, Plan Assets, Amount | $ 0 | $ 0 | |
Hedge Funds | Minimum | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Investment Redemption, Notice Period | 10 days | | |
Hedge Funds | Maximum | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Investment Redemption, Notice Period | 45 days | | |