Consolidated Statement of Stockholders' Equity (Unaudited) - 6 months ended Jun. 30, 2015 - USD ($) $ in Thousands		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, 2014		$ 817,415	$ 25	$ 202,676	$ 523,541	$ 91,173
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased			0	(1,443)
Shares issued for stock-based awards			0	1,375
Compensation expense and related tax benefit for stock-based award grants				881
Net income		38,697			38,697
Dividends on common stock ($0.42 per share)					(10,503)
Change in net unrealized investment appreciation	[1]					(16,909)
Change in liability for underfunded employee benefit plans	[2]					2,427
All other changes in stockholders’ equity accounts		(24,172)
Balance, end of period at Jun. 30, 2015		$ 831,940	$ 25	$ 203,489	$ 551,735	$ 76,691

[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.