Schedule II - Condensed Financial Information of Registrant - Condensed Statements of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 72,988us-gaap_NetIncomeLoss	$ 58,977us-gaap_NetIncomeLoss	$ 30,312us-gaap_NetIncomeLoss
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of share-based compensation	12,342us-gaap_ShareBasedCompensation	6,417us-gaap_ShareBasedCompensation	3,830us-gaap_ShareBasedCompensation
Amortization of original issue discount on debt	840	601
Accretion of deferred credit	(840)us-gaap_AccretionExpense	(601)us-gaap_AccretionExpense
Net realized (gains) losses on investments	(5,627)	14,740	11,943
Net change in unrealized (gains) losses on investments		(7,850)	(9,443)
Deferred income taxes	1,118	7,363	3,813
Excess tax benefits from share-based compensation	(7,006)	(359)	1,760
Other	19us-gaap_OtherNoncashIncomeExpense	10us-gaap_OtherNoncashIncomeExpense	5us-gaap_OtherNoncashIncomeExpense
Net change in assets and liabilities relating to operating activities:
Restricted cash and cash equivalents	(35)	30,409	45,304
Purchases of equity securities, trading		(26,009)	(343,962)
Proceeds from sale of equity securities, trading		102,661	360,000
Income taxes recoverable	2,477	(5,558)	(2,594)
Income taxes payable	6,239	2,226	(13,801)
Net cash provided by (used in) operating activities	123,346	156,959	142,506
Cash flows from investing activities:
Purchases of equity securities, available for sale	(116,541)	(77,859)
Purchases of fixed maturities, available for sale	(106,885)	(305,330)
Proceeds from sales of equity securities, available for sale	163,981	15,542
Proceeds from sales of fixed maturities, available for sale	17,153
Net cash provided by (used in) investing activities	(77,188)	(352,683)	(2,698)
Cash flows from financing activities:
Proceeds from borrowings		20,000
Repayment of debt	(7,471)us-gaap_RepaymentsOfDebt	(1,471)us-gaap_RepaymentsOfDebt	(1,471)us-gaap_RepaymentsOfDebt
Preferred stock dividend	(13)	(29)	(287)
Common stock dividend	(19,240)us-gaap_PaymentsOfDividendsCommonStock	(17,725)us-gaap_PaymentsOfDividendsCommonStock	(18,669)us-gaap_PaymentsOfDividendsCommonStock
Issuance of common stock	73		207
Purchase of treasury stock	(29,736)	(32,366)
Payments related to tax withholding for share-based compensation	(17,655)	(3,161)	(121)
Excess tax benefits (shortfall) from share-based compensation	7,006	359	(1,760)
Net cash provided by (used in) financing activities	(48,036)	(34,393)	(22,101)
Net increase (decrease) in cash and cash equivalents	(1,878)	(230,117)	117,707
Cash and cash equivalents at beginning of period	117,275	347,392	229,685
Cash and cash equivalents at end of period	115,397	117,275	347,392
Parent Company [Member]
Cash flows from operating activities:
Net income	72,988	58,977	30,312
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in net income of subsidiaries	(94,924)	(78,600)	(38,916)
Distribution of income from subsidiaries	55,805	26,898	40,222
Depreciation	2
Amortization of share-based compensation	12,342	6,417	3,830
Amortization of original issue discount on debt	840	601
Accretion of deferred credit	(840)	(601)
Net realized (gains) losses on investments	(625)	2,947	1,880
Net change in unrealized (gains) losses on investments		(1,625)	(1,162)
Deferred income taxes	1,118	7,363	3,813
Excess tax benefits from share-based compensation	(7,006)	(359)	1,760
Net change in assets and liabilities relating to operating activities:
Restricted cash and cash equivalents			30,220
Purchases of equity securities, trading		(3,972)	(58,836)
Proceeds from sale of equity securities, trading		16,712	60,379
Income taxes recoverable	2,477	(5,558)	(2,594)
Income taxes payable	6,239	2,226	(13,801)
Other operating assets and liabilities	5,752	1,347	2,911
Net cash provided by (used in) operating activities	54,168	32,773	60,018
Cash flows from investing activities:
Capital contributions to subsidiaries	(5,585)	(1,600)	(28,555)
Purchases of equity securities, available for sale	(15,836)	(10,357)
Purchases of fixed maturities, available for sale	(3,000)	(750)
Proceeds from sales of equity securities, available for sale	26,060
Proceeds from sales of fixed maturities, available for sale	770
Net cash provided by (used in) investing activities	2,409	(12,707)	(28,555)
Cash flows from financing activities:
Proceeds from borrowings		20,000
Repayment of debt	(6,000)
Preferred stock dividend	(13)	(29)	(287)
Common stock dividend	(19,240)	(17,725)	(18,669)
Issuance of common stock	73		207
Purchase of treasury stock	(29,736)	(32,365)
Proceeds received from issuance of common and contingently redeemable common stock	19,000
Payments related to tax withholding for share-based compensation	(17,655)	(3,161)	(121)
Excess tax benefits (shortfall) from share-based compensation	7,006	359	(1,760)
Net cash provided by (used in) financing activities	(46,565)	(32,921)	(20,630)
Net increase (decrease) in cash and cash equivalents	10,012	(12,855)	10,833
Cash and cash equivalents at beginning of period	4,878	17,733	6,900
Cash and cash equivalents at end of period	$ 14,890	$ 4,878	$ 17,733

Amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values. Excludes accretion associated with asset retirement obligations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section 35

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6394232&loc=d3e17558-110866