Losses And Loss Adjustment Expense Reserves - Incurred and Paid Claims (Details)	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 ($)	Dec. 31, 2007 USD ($)
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 193,271,387
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	25,076,171,000
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	156,930,790
Short-duration Insurance Contracts, Accident Year 2007 [Member]
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	24,023,109,000	$ 23,979,026,000	$ 24,107,044,000	$ 24,770,214,000	$ 25,511,988,000	$ 26,203,117,000	$ 27,029,577,000	$ 27,061,323,000	$ 26,117,669,000	$ 24,747,856,000
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	$ 0
Cumulative Number of Reported Claims	1,013
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 24,023,106,000	23,907,436,000	23,906,841,000	23,762,758,000	23,548,201,000	23,333,861,000	21,637,121,000	18,309,573,000	12,283,217,000	$ 6,980,915,000
Short-duration Insurance Contracts, Accident Year 2008 [Member]
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	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	$ 17,593,260,000	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 [Member]
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	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	$ 842,316,000
Cumulative Number of Reported Claims	1,013
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 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 [Member]
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	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	$ 682,675,000
Cumulative Number of Reported Claims	974
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 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 [Member]
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	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	$ 642,817,000
Cumulative Number of Reported Claims	1,020
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 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 [Member]
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	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	$ 794,910,000
Cumulative Number of Reported Claims	961
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 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 [Member]
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	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	$ 1,430,773,000
Cumulative Number of Reported Claims	839
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 19,067,334,000	14,319,057,000	10,656,777,000	$ 7,594,731,000
Short-duration Insurance Contracts, Accident Year 2014 [Member]
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	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	$ 3,433,848,000
Cumulative Number of Reported Claims	732
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 9,173,947,000	6,082,893,000	$ 3,826,263,000
Short-duration Insurance Contracts, Accident Year 2015 [Member]
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	20,840,034,000	20,452,199,000
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	$ 6,440,742,000
Cumulative Number of Reported Claims	686
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 11,151,955,000	$ 6,263,796,000
Short-duration Insurance Contracts, Accident Year 2016 [Member]
Claims Development [Line Items]
Cumulative Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	21,646,663,000
Total of Incurred But Not Reported Liabilities Plus Expected Development on Reported Claims	$ 10,808,090,000
Cumulative Number of Reported Claims	696
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance	$ 7,435,120,000