Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Net Cash Provided by (Used in) Operating Activities [Abstract]
Net Cash Provided by (Used in) Operating Activities	$ 300,822	$ 206,412
Cash flows from investing activities:
Proceeds from Sale and Maturity of Fixed-Maturity Investments Available-for-sale	348,082	649,687
Proceeds from Sale of Equity Securities	82,701	18,103
Proceeds from Sale of Trading Securities Held-for-investment	16,639	130,022
Proceeds from Redemption of Fixed-Maturity Investments Available-for-sale	219,825	260,848
Proceeds from Redemption of Trading Securities Held-for-investment	33,849	43,603
Purchases of Fixed-Maturity Investments Available-for-sale	(807,204)	(1,147,875)
Purchases of Equity Securities	(52,357)	(193,409)
Sales, Redemptions and (Purchases) of Short-term Investments, Net	(205,566)	201,942
Sales, Redemptions and (Purchases) of Other assets and other invested assets, net	293	412
Purchases of property and equipment, net	(12,328)	(13,444)
Acquisitions, net of cash acquired	(634)	(86)
Net cash provided by (used in) investing activities	(376,700)	(50,197)
Cash flows from financing activities:
Dividends paid	(1,073)	(1,076)
Purchases and redemptions of senior notes	0	(141,686)
Proceeds from termination of capped calls	0	4,083
Issuance of common stock	810	3,123
Purchase of common shares	(50,053)	(6)
Credit facility commitment fees paid	(405)	0
Change in secured borrowings (Note 12)	119,631	0
Proceeds from secured borrowings (with terms greater than 3 months)	15,544	0
Repayment of other borrowings	(94)	(140)
Net cash provided by (used in) financing activities	84,360	(135,702)
Effect of exchange rate changes on cash and restricted cash	(1)	77
Increase (decrease) in cash and restricted cash	8,481	20,590
Cash and restricted cash, beginning of period	96,244	61,814
Cash and restricted cash, end of period	$ 104,725	$ 82,404