CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Statement Of Cash Flows [Abstract]
Cash flows from operating activities	$ 178,637	$ 241,182
Cash flows from investing activities:
Proceeds from sale of property and equipment	31	55
Purchases of property and equipment	(6,041)	(10,310)
Payments to acquire a business		(1,000)
Purchases of equity securities	(46,414)	(46,668)
Purchases of fixed maturities	(278,961)	(145,118)
Purchases of short-term investments		(87,538)
Purchases of investment real estate, net	(4,400)	(5,888)
Proceeds from sales of equity securities	46,819	17,412
Proceeds from sales of fixed maturities	78,966	26,154
Proceeds from sales of short-term investments		12,500
Maturities of fixed maturities	38,111	63,201
Maturities of short-term investments	25,000	50,000
Net cash provided by (used in) investing activities	(146,889)	(127,200)
Cash flows from financing activities:
Preferred stock dividend	(7)	(7)
Common stock dividend	(9,828)	(8,520)
Issuance of common stock		511
Purchase of treasury stock	(8,415)	(7,665)
Sale of treasury stock	2,965
Purchase of preferred stock		(257)
Payments related to tax withholding for share-based compensation	(4,905)	(10,195)
Excess tax benefits (shortfall) from share-based compensation	(1,563)	5,241
Borrowings under promissory note		1,390
Repayment of debt	(1,768)	(8,103)
Net cash provided by (used in) financing activities	(23,521)	(27,605)
Net increase (decrease) in cash and cash equivalents	8,227	86,377
Cash and cash equivalents at beginning of period	197,014	115,397
Cash and cash equivalents at end of period	205,241	201,774
Supplemental cash and non-cash flow disclosures:
Interest paid	362	767
Income taxes paid	58,268	$ 51,554
Income tax refund	$ 5,694