Consolidated Statement of Stockholders' Equity (Unaudited) (USD $) In Thousands, unless otherwise specified		Total	Common Stocks [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income, Net of Tax [Member]
Balance, beginning of year at Dec. 31, 2012		$ 729,177	$ 25	$ 208,536	$ 425,428	$ 95,188
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Compensation expense and related tax benefit for stock-based award grants				1,010
Shares repurchased			0	(99)
Shares issued for stock-based awards			0	3,075
Net income		49,614			49,614
Dividends on common stock ($0.51 per share)					(12,910)
Change in net unrealized investment appreciation	[1]					(28,500)
Change in liability for underfunded employee benefit plans	[2]					2,860
All other changes in stockholders’ equity accounts		(34,564)
Balance, end of year at Sep. 30, 2013		$ 744,227	$ 25	$ 212,522	$ 462,132	$ 69,548

[1] The change in net unrealized appreciation is net of reclassification adjustments and income taxes.

[2] The change in liability for underfunded employee benefit plans is net of reclassification adjustments and income taxes.