Condensed Financial Information - Statement of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating activities:
Net income	$ 63,762	$ 25,597	$ 69,578
Adjustments to reconcile net income to net cash provided by (used in) operations:
Other	36,503	19,569	4,656
Net cash provided by (used in) operating activities	96,739	118,338	118,221
Fixed maturities, available-for-sale
Sales	1,319,404	666,976	1,191,796
Purchases	(1,711,080)	(803,568)	(1,439,725)
Equity securities
Sales	39,503	73,590	6,942
Net increase in short-term investments	(31,568)	30,384	22,713
Net cash provided by (used in) investing activities	(179,839)	66,006	(36,461)
Financing activities:
Purchase of treasury stock		(90,866)	(51,980)
Proceeds of stock issued from employee stock purchase plan	672	945	868
Proceeds of stock issued from exercise of stock options	404	1,169	611
Net cash provided by (used in) financing activities	1,076	(88,752)	(50,501)
Cash at beginning of year	127,360	31,768	509
Cash at end of period	45,336	127,360	31,768
Parent Company
Operating activities:
Net income	63,762	25,597	69,578
Adjustments to reconcile net income to net cash provided by (used in) operations:
Equity in undistributed net income of wholly-owned subsidiaries	(70,036)	(32,524)	(74,914)
Dividends received from subsidiaries	15,000	45,000	40,000
Other	(3,265)	5,831	4,543
Net cash provided by (used in) operating activities	5,461	43,904	39,207
Fixed maturities, available-for-sale
Sales	7,986	45,716	26,313
Purchases	(14,700)	(9,253)	(28,213)
Equity securities
Sales			2,995
Purchases			(2,367)
Net increase in short-term investments	(167)	10,064	5,122
Net cash provided by (used in) investing activities	(6,881)	46,527	3,850
Financing activities:
Capital contribution
Purchase of treasury stock		(90,866)	(51,980)
Proceeds of stock issued from employee stock purchase plan	672	945	868
Proceeds of stock issued from exercise of stock options	404	1,169	611
Net cash provided by (used in) financing activities	1,076	(88,752)	(50,501)
Increase (decrease) in cash	(344)	1,679	(7,444)
Cash at beginning of year	3,325	1,646	9,090
Cash at end of period	$ 2,981	$ 3,325	$ 1,646