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				333
Shares issued for stock-based awards			0	603
Net income		22,393			22,393
Dividends on common stock ($0.15 per share)					(3,786)
Change in net unrealized investment appreciation	[1]					8,614
Change in liability for underfunded employee benefit plans	[2]					808
All other changes in stockholders’ equity accounts		6,572
Balance, end of year at Mar. 31, 2013		$ 758,142	$ 25	$ 209,472	$ 444,035	$ 104,610

[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 income taxes.