XML 117 R31.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Tables) | 12 Months Ended
--- | ---
Dec. 31, 2019
Accounting Policies [Abstract] |
Summary of Deferred Policy Acquisition Cost Amortization and Net Advertising Expense | The table below presents a summary of deferred policy acquisition cost amortization and net advertising expense:
| Year Ended December 31,
| 2019 |  | 2018 |  | 2017
| (Amounts in millions)
Deferred policy acquisition cost amortization | $ | 602.1 |  |  | $ | 572.2 |  |  | $ | 555.4 |
Net advertising expense | 42.2 |  |  | 40.9 |  |  | 37.4 |

X
- Definition Summary of Deferred Policy Acquisition Cost Amortization and Net Advertising Expense [Table Text Block] + References No definition available. + Details
Name: | mcy_SummaryofDeferredPolicyAcquisitionCostAmortizationandNetAdvertisingExpenseTableTextBlock
Namespace Prefix: | mcy_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_AccountingPoliciesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration