Debt (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Long-term debt [Abstract]
Carrying Value	$ 216,118,000	$ 261,973,000	$ 216,118,000	$ 261,973,000	$ 263,119,000
Fair Value Level 2	224,902,000	255,065,000	224,902,000	255,065,000	252,702,000
Issuance of senior unsecured notes			0	100,000,000
Net proceeds from issuance of notes				99,100,000
Percentage principal amount to offered to repurchase notes (in hundredths)			101.00%
Shelf registration statement remaining amount	400,000,000		400,000,000
Estimated fair value of debt	224,902,000	255,065,000	224,902,000	255,065,000	252,702,000
Issuance cost of senior notes			900,000
Debentures repurchased (in shares)	645,779	0	646,008	0
Debentures repurchased (face value)	64,600,000	0	64,600,000	0
Debentures repurchased (loss in dollars)	6,300,000	0	6,300,000	0
5.5% Senior notes [Member] | Level 2 [Member]
Long-term debt [Abstract]
Carrying Value	99,000,000	99,000,000	99,000,000	99,000,000	99,000,000
Fair Value Level 2	100,832,000	100,643,000	100,832,000	100,643,000	100,733,000
Senior unsecured notes maturity date			May 15, 2013
Estimated fair value of debt	100,832,000	100,643,000	100,832,000	100,643,000	100,733,000
Effective interest rate (in hundredths)	5.50%	5.50%	5.50%	5.50%	5.50%
5.875% Senior notes [Member] | Level 2 [Member]
Long-term debt [Abstract]
Carrying Value	100,000,000	100,000,000	100,000,000	100,000,000	100,000,000
Fair Value Level 2	104,458,000	96,120,000	104,458,000	96,120,000	93,070,000
Senior unsecured notes maturity date			Jun. 01, 2021
Estimated fair value of debt	104,458,000	96,120,000	104,458,000	96,120,000	93,070,000
Effective interest rate (in hundredths)	5.875%	5.875%	5.875%	5.875%	5.875%
0% Subordinated debentures [Member] | Level 2 [Member]
Long-term debt [Abstract]
Carrying Value	17,118,000	62,973,000	17,118,000	62,973,000	64,119,000
Fair Value Level 2	19,612,000	58,302,000	19,612,000	58,302,000	58,899,000
Senior unsecured notes maturity date			Dec. 31, 2015
Estimated fair value of debt	$ 19,612,000	$ 58,302,000	$ 19,612,000	$ 58,302,000	$ 58,899,000
Effective interest rate (in hundredths)	7.45%	7.45%	7.45%	7.45%	7.45%