Consolidated Statement of Stockholders' Equity (Unaudited) - 3 months ended Mar. 31, 2016 - USD ($) $ in Thousands		Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income, Net of Tax [Member]
Balance, beginning of year at Dec. 31, 2015		$ 878,897	$ 25	$ 207,426	$ 591,009	$ 80,437
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Compensation expense and related tax benefit for stock-based award grants				313
Shares issued for stock-based awards			0	4,745
Net income		22,427			22,427
Dividends on common stock ($0.22 per share)					(5,553)
Change in net unrealized investment appreciation	[1]					27,449
Change in liability for underfunded employee benefit plans	[2]					891
All other changes in stockholders’ equity accounts		27,845
Balance, end of period at Mar. 31, 2016		$ 929,169	$ 25	$ 212,484	$ 607,883	$ 108,777

[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.