Schedule II Condensed Financial Information of Registrant (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
ASSETS
Other assets	$ 277,350		$ 228,264
Total assets	9,768,527		8,826,672		8,167,726
LIABILITIES AND SHAREHOLDERS' EQUITY
Long-term debt, current and noncurrent	199,939		199,874
Other liabilities	422,362		366,013
Total liabilities	8,432,064		7,727,367
Preferred stock, $0.001 par value, authorized 1,000,000 shares; none issued	0		0
Common stock, $0.001 par value, authorized 75,000,000 shares; issued, 2014, 64,245,048; 2013, 63,629,105	64		64
Additional paid-in capital	422,232		407,056
Retained earnings	1,065,318		1,000,312
Accumulated other comprehensive income (loss), net of taxes:
Net unrealized gains on fixed maturities and equity securities	297,554	[1],[2]	133,990	[1],[2]	382,400	[1],[2]
Net funded status of pension and other postretirement benefit obligations	(12,953)	[1]	(11,776)	[1]	(15,311)	[1]
Treasury stock, at cost, 2014, 23,308,430 shares; 2013, 23,117,554 shares	(435,752)		(430,341)
Total shareholders equity	1,336,463		1,099,305		1,245,803
Total liabilities and shareholders equity	9,768,527		8,826,672
Parent Company [Member]
ASSETS
Investments and cash	28,640		24,387
Investment in subsidiaries	1,515,769		1,282,614
Other assets	58,365		60,164
Total assets	1,602,774		1,367,165
LIABILITIES AND SHAREHOLDERS' EQUITY
Short-term debt	38,000		38,000
Long-term debt, current and noncurrent	199,939		199,874
Other liabilities	28,372		29,986
Total liabilities	266,311		267,860
Preferred stock, $0.001 par value, authorized 1,000,000 shares; none issued	0		0
Common stock, $0.001 par value, authorized 75,000,000 shares; issued, 2014, 64,245,048; 2013, 63,629,105	64		64
Additional paid-in capital	422,232		407,056
Retained earnings	1,065,318		1,000,312
Accumulated other comprehensive income (loss), net of taxes:
Net unrealized gains on fixed maturities and equity securities	297,554		133,990
Net funded status of pension and other postretirement benefit obligations	(12,953)		(11,776)
Treasury stock, at cost, 2014, 23,308,430 shares; 2013, 23,117,554 shares	(435,752)		(430,341)
Total shareholders equity	1,336,463		1,099,305
Total liabilities and shareholders equity	$ 1,602,774		$ 1,367,165

[1] All amounts are net of tax.

[2] The pretax amounts reclassified from accumulated other comprehensive income, $10,943 and $22,245, are included in net realized investment gains and losses and the related tax expenses, $3,830 and $7,786, are included in income tax expense in the Consolidated Statements of Operations for the years ended December 31, 2014 and 2013, respectively.