Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Deferred tax asset:
Loss reserve discounting	$ 86,659,000	$ 100,806,000
Unearned premiums	187,522,000	176,465,000
Other-than-temporary impairments	26,139,000	26,509,000
Restricted stock units	72,889,000	62,442,000
Other	104,130,000	89,761,000
Gross deferred tax asset	477,339,000	455,983,000
Less valuation allowance	(5,457,000)	(4,037,000)
Deferred tax asset	471,882,000	451,946,000
Deferred tax liability:
Amortization of intangibles	21,192,000	20,316,000
Deferred policy acquisition costs	173,481,000	162,344,000
Unrealized investment gains	238,232,000	115,499,000
Deferred Tax Liabilities, Property, Plant and Equipment	34,857,000	33,398,000
Deferred Tax Liabilities, Investments	85,075,000	79,124,000
Other	53,410,000	48,076,000
Deferred tax liability	606,247,000	458,757,000
Net deferred tax liability	134,365,000	6,811,000
Current federal income taxes	14,768,000	55,763,000
Operating Loss Carryforwards [Line Items]
Taxes Payable, Current		55,763,000
Tax Credit Carryforward, Valuation Allowance	5,500,000	$ 4,000,000
Foreign Tax Authority (expiration 2031) [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	5,300,000
Foreign Tax Authority (No expiration) [Member] [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 29,900,000