Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Cash Provided by (Used in) Operating Activities	$ 491,929	$ 218,425
Cash flows from investing activities:
Proceeds from Sales of Fixed-Maturity Investments Available-for-sale	577,034	737,054
Proceeds from Sales of Trading Securities	35,182	176,448
Proceeds from Sales of Equity Securities	92,702	23,423
Proceeds from Redemption of Fixed-Maturity Investments Available for sale	337,857	377,219
Proceeds from Redemptions of Trading securities	53,437	70,161
Purchases of Fixed-Maturity Investments Available-for-sale	(1,307,335)	(1,491,083)
Purchases of Equity Securities	(59,625)	(195,297)
Sales, Redemptions and (Purchases) of Short-term Investments, Net	(216,778)	251,509
Sales, Redemptions and (Purchases) of Other assets and other invested assets, net	2,111	596
Purchases of property and equipment, net	(20,323)	(25,173)
Acquisitions, net of cash acquired	(662)	(86)
Net cash provided by (used in) investing activities	(506,400)	(75,229)
Cash flows from financing activities:
Dividends paid	(1,606)	(1,614)
Issuance of senior notes, net	0	443,250
Purchases and redemptions of senior notes	0	(591,918)
Proceeds from termination of capped calls	0	4,109
Issuance of common stock	1,128	3,283
Purchase of common shares	(50,053)	(6)
Credit facility commitment fees paid	(643)	0
Change in secured borrowings (Note 12)	41,414	36,782
Proceeds from secured borrowings (with terms greater than 3 months)	45,458	0
Payments of secured borrowings (with terms greater than 3 months)	(3,000)	0
Repayment of other borrowings	(133)	(207)
Net cash provided by (used in) financing activities	32,565	(106,321)
Effect of exchange rate changes on cash and restricted cash	0	116
Increase (decrease) in cash and restricted cash	18,094	36,991
Cash and restricted cash, beginning of period	96,244	61,814
Cash and restricted cash, end of period	$ 114,338	$ 98,805