CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 355,761	$ 342,517	$ 1,172,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and other amortization	64,430	61,342	52,559
Deferred tax expense (benefit)	355,044	162,356	(692,810)
Net realized investment gains	(249)	(8,932)	(28,361)
Loss on debt extinguishment	65	90,531	507
Change in certain assets and liabilities:
Accrued investment income	(1,987)	(3,849)	(9,706)
Prepaid reinsurance premium	11	101	47,457
Reinsurance recoverable on loss reserves	2,019	(6,006)	13,354
Reinsurance recoverable on paid losses	1,092	(1,645)	3,105
Premiums receivable	(1,653)	(3,923)	8,973
Deferred insurance policy acquisition costs	(1,082)	(2,518)	(3,001)
Profit commission receivable	(2,844)	(747)	64,525
Loss reserves	(453,178)	(454,589)	(503,405)
Premium deficiency reserve	0	0	(23,751)
Unearned premiums	63,197	49,764	76,559
Return premium accrual	(25,400)	(18,800)	(9,600)
Income taxes payable - current	49,178	1,123	2,518
Other, net	2,253	18,035	(9,528)
Net cash provided by operating activities	406,657	224,760	161,395
Purchases of investments:
Fixed income	(1,293,616)	(1,360,386)	(2,462,844)
Equity securities	(79)	(3,197)	(2,623)
Proceeds from sales of fixed income	246,908	728,042	1,796,153
Proceeds from maturity of fixed income	759,212	547,444	559,774
Proceeds from sale of equity securities	0	5,257	0
Net increase in restricted cash	0	0	17,212
Additions to property and equipment	(16,066)	(10,552)	(4,630)
Net cash used in investing activities	(303,641)	(93,392)	(96,958)
Cash flows from financing activities:
Proceeds from revolving credit facility	150,000	0	0
Repayment of revolving credit facility	(150,000)	0	0
Proceeds from issuance of long-term debt	0	573,094	0
Repayment of long-term debt	0	0	(61,953)
Purchase or repayment of convertible senior notes	(145,620)	(363,778)	(11,152)
Payment of original issue discount - convertible senior notes	(4,504)	(11,250)	(345)
Purchase of convertible junior subordinated debentures	0	(100,860)	0
Payment of original issue discount-convertible junior subordinated debentures	0	(41,540)	0
Cash portion of loss on debt extinguishment	0	(59,460)	(507)
Repurchase of common stock	0	(147,127)	0
Payment of debt issuance costs	(1,630)	(1,127)	0
Payment of withholding taxes related to share-based compensation net share settlement	(6,821)	(5,030)	(7,242)
Net cash used in financing activities	(158,575)	(157,078)	(81,199)
Net decrease in cash and cash equivalents	(55,559)	(25,710)	(16,762)
Cash and cash equivalents at beginning of year	155,410	181,120	197,882
Cash and cash equivalents at end of year	$ 99,851	$ 155,410	$ 181,120