Schedule III - Supplementary Insurance Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	$ 92,651	$ 109,262	$ 112,024
Reverse for Losses and Loss Adjustment Expenses	7,940,720	7,843,856	7,653,229
Unearned Premium Reserves	1,349,799	1,442,122	1,317,147
Premiums Earned	2,143,760	2,113,726	2,006,361
Net Investment Income	273,253	290,310	296,996
Incurred Loss and Loss Adjustment Expenses	1,319,561	1,354,093	1,272,156
Amortization of Deferred Acquisition Costs	315,069	339,402	293,922
Other Operating Expenses	214,819	192,032	193,499
Net Written Premium	2,093,283	2,106,974	2,117,377
Domestic [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	68,055	79,674	85,098
Reverse for Losses and Loss Adjustment Expenses	6,033,374	6,005,952	5,908,051
Unearned Premium Reserves	1,059,530	1,078,384	1,041,653
Premiums Earned	1,562,544	1,512,762	1,414,666
Net Investment Income	239,072	250,048	252,671
Incurred Loss and Loss Adjustment Expenses	924,742	996,055	956,233
Amortization of Deferred Acquisition Costs	193,911	219,747	179,591
Other Operating Expenses	180,516	157,429	159,589
Net Written Premium	1,530,592	1,494,731	1,507,293
International [Member]
Supplementary Insurance Information, by Segment [Line Items]
Deferred Acquisition Costs	24,596	29,588	26,926
Reverse for Losses and Loss Adjustment Expenses	1,907,346	1,837,904	1,745,178
Unearned Premium Reserves	290,269	363,738	275,494
Premiums Earned	581,216	600,964	591,695
Net Investment Income	34,181	40,262	44,325
Incurred Loss and Loss Adjustment Expenses	394,819	358,038	315,923
Amortization of Deferred Acquisition Costs	121,158	119,655	114,331
Other Operating Expenses	34,303	34,603	33,910
Net Written Premium	$ 562,691	$ 612,243	$ 610,084