Losses And Loss Adjustment Expense Reserves - Incurred and Paid Claims (Details)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 196,783,974	$ 193,271,387
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	25,697,802,000
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	157,445,399	156,930,790
Short-duration Insurance Contracts, Accident Year 2008
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	17,497,508,000	17,617,589,000	$ 17,456,810,000	$ 17,889,384,000	$ 18,668,518,000	$ 19,347,265,000	$ 20,004,073,000	$ 21,290,931,000	$ 22,106,937,000	$ 22,580,220,000
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative number of reported claims	921
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 17,497,105,000	17,593,260,000	17,178,322,000	17,041,185,000	17,001,061,000	16,856,762,000	15,902,618,000	13,950,969,000	9,869,827,000	$ 6,962,996,000
Short-duration Insurance Contracts, Accident Year 2009
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	17,622,828,000	18,554,526,000	19,050,348,000	19,667,376,000	20,398,961,000	21,012,811,000	21,571,780,000	21,412,289,000	21,751,337,000
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	$ 1,208,000
Cumulative number of reported claims	1,013
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 17,568,877,000	17,550,304,000	17,380,065,000	17,336,454,000	17,121,818,000	16,180,346,000	13,160,200,000	9,592,059,000	$ 4,919,359,000
Short-duration Insurance Contracts, Accident Year 2010
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	16,828,688,000	17,641,161,000	18,075,737,000	18,639,537,000	19,326,007,000	19,883,812,000	20,437,443,000	21,418,368,000
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	$ 5,944,000
Cumulative number of reported claims	974
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 16,720,942,000	16,778,214,000	16,283,050,000	15,330,864,000	14,756,510,000	12,955,467,000	10,695,223,000	$ 7,535,122,000
Short-duration Insurance Contracts, Accident Year 2011
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	19,187,240,000	18,224,634,000	17,879,595,000	17,014,895,000	17,605,460,000	17,900,250,000	18,120,563,000
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	$ 107,793,000
Cumulative number of reported claims	1,021
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 19,027,232,000	17,422,583,000	16,115,802,000	14,251,525,000	11,212,490,000	8,608,287,000	$ 4,719,943,000
Short-duration Insurance Contracts, Accident Year 2012
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	17,914,837,000	18,050,131,000	18,344,175,000	18,895,666,000	19,532,022,000	18,511,598,000
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	$ 125,157,000
Cumulative number of reported claims	965
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 17,265,513,000	16,734,967,000	15,369,629,000	13,411,125,000	11,673,621,000	$ 6,719,982,000
Short-duration Insurance Contracts, Accident Year 2013
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	22,798,398,000	21,742,580,000	20,323,841,000	20,118,343,000	19,570,946,000
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	$ 1,049,748,000
Cumulative number of reported claims	845
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 21,415,490,000	19,067,334,000	14,319,057,000	10,656,777,000	$ 7,594,731,000
Short-duration Insurance Contracts, Accident Year 2014
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	17,640,211,000	14,930,960,000	15,394,995,000	16,884,731,000
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	$ 1,616,118,000
Cumulative number of reported claims	742
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 14,556,687,000	9,173,947,000	6,082,893,000	$ 3,826,263,000
Short-duration Insurance Contracts, Accident Year 2015
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	22,471,512,000	20,840,034,000	20,452,199,000
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	$ 4,412,589,000
Cumulative number of reported claims	717
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 14,978,639,000	11,151,955,000	$ 6,263,796,000
Short-duration Insurance Contracts, Accident Year 2016
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	22,908,016,000	21,646,663,000
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	$ 7,070,782,000
Cumulative number of reported claims	763
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 12,009,273,000	$ 7,435,120,000
Short-duration Insurance Contracts, Accident Year 2017
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	21,914,736,000
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	$ 11,308,463,000
Cumulative number of reported claims	706
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 6,405,641,000