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Debt - Narrative (Details) - USD ($) |  | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Aug. 03, 2016 | Mar. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 30, 2016
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Repayments of long-term debt (in US dollars) |  |  |  | $ 15,235,000 | $ 15,202,000 | $ 417,990,000 |
Letters of credit outstanding (in US dollars) |  |  |  | 109,000,000 | 110,100,000 |  |
Borrowings under revolving credit facility (in US dollars) |  |  |  | $ 25,000,000 | 25,000,000 |  |
2016 Credit Agreement |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Credit agreement, initiation date | Aug. 03, 2016 |  |  |  |  |  |
Expiration date of credit agreement |  |  |  | Aug. 03, 2021 |  |  |
Interest rate description |  |  |  | Borrowings under the 2016 Credit Agreement bear interest at (1) a base rate plus a margin of 0.00% to 0.75%, based on certain financial tests, or (2) United States dollar LIBOR (2.52% at December 31, 2018) plus 1.00% to 1.75%, based on certain financial tests. The base rate is determined by the greater of (a) the prime commercial lending rate announced by Bank of Montreal from time to time (5.50% at December 31, 2018), (b) the federal funds effective rate, plus ½ of 1.00%, (c) the daily one month LIBOR rate, plus 1.00%, or (d) 0.00%. The interest rate in effect at December 31, 2018 was 3.52%. Fees for letters of credit issued under the 2016 Revolving Credit Facility range from 1.00% to 1.75% of the respective face amounts of outstanding letters of credit and are computed based on certain financial tests. |  |  |
Interest rate |  |  |  | 3.52% |  |  |
2016 Term Loan |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Term Loan (in US dollars) | $ 400,000,000 |  |  | $ 269,620,000 | 284,810,000 |  |
Periodic principal payments on term loan (in US dollars) |  | $ 3,800,000 | $ 5,000,000.0 |  |  | 5,000,000 |
Term loan, annual principal payments (in US dollars) |  |  |  |  |  |  | $ 100,000,000
Repayments of long-term debt (in US dollars) |  |  |  |  |  | $ 95,000,000 |
Base Rate | Minimum | 2016 Credit Agreement |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  | 0.00% |  |  |
Base Rate | Maximum | 2016 Credit Agreement |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  | 0.75% |  |  |
Prime Rate, Bank of Montreal | 2016 Credit Agreement |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Commercial lending rate |  |  |  | 5.50% |  |  |
Credit Agreement Base Rate, Daily One Month LIBOR Rate | 2016 Credit Agreement |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  | 1.00% |  |  |
London Interbank Offered Rate (LIBOR) | 2016 Credit Agreement |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Commercial lending rate |  |  |  | 2.52% |  |  |
London Interbank Offered Rate (LIBOR) | Minimum | 2016 Credit Agreement |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  | 1.00% |  |  |
London Interbank Offered Rate (LIBOR) | Maximum | 2016 Credit Agreement |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  | 1.75% |  |  |
Credit Agreeement Base Rate, Federal Funds Rate | 2016 Credit Agreement |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  | 0.50% |  |  |
Credit Agreement, 0% Base Rate | 2016 Credit Agreement |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Commercial lending rate |  |  |  | 0.00% |  |  |
Revolving Credit Facility | 2016 Revolving Credit Facility |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Line of credit facility maximum borrowing capacity (in US dollars) | $ 900,000,000 |  |  |  |  |  |
Increase in borrowing capacity (in US dollars) |  |  |  | $ 1,300,000,000 |  |  |
Letters of credit maximum borrowing capacity (in US dollars) |  |  |  | $ 300,000,000 |  |  |
Commitment fee percentage of unused amount |  |  |  | 0.15% |  |  |
Borrowings under revolving credit facility (in US dollars) |  |  |  | $ 25,000,000 | $ 25,000,000 |  |
Revolving Credit Facility | Minimum | 2016 Revolving Credit Facility |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Commitment fee percentage of unused amount |  |  |  | 0.15% |  |  |
Letter of credit fees |  |  |  | 1.00% |  |  |
Revolving Credit Facility | Maximum | 2016 Revolving Credit Facility |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |
Commitment fee percentage of unused amount |  |  |  | 0.30% |  |  |
Letter of credit fees |  |  |  | 1.75% |  |  |

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- Definition Amount of increase in borrowing capacity if additional lenders are identified and/or existing lenders are willing to increase their current commitments. + References No definition available. + Details
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- Definition Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6036836-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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