Debt (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jul. 02, 2012	May 30, 2012	Dec. 31, 2011
Long-term debt [Abstract]
Fair Value Level 2	$ 276,089,000	$ 258,851,000	$ 276,089,000	$ 258,851,000			$ 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%
Debt issuance shelf registration statement filed amount						500,000,000
Face amount of repurchased debentures					64,100,000
Shelf registration statement remaining amount	400,000,000		400,000,000
Estimated fair value of debt	276,089,000	258,851,000	276,089,000	258,851,000			252,702,000
Effective interest rate (in hundredths)	7.45%		7.45%
Issuance cost of senior notes			900,000
Debentures repurchased (in shares)	0	0	229	0
Debentures repurchased (face value)	0	0	22,900	0
Debentures repurchased (loss in dollars)	0	0	1,000	0
5.5% Senior notes [Member]
Long-term debt [Abstract]
Senior unsecured notes annual interest rate (in hundredths)	5.50%		5.50%
Senior unsecured notes maturity date			May 15, 2013
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	100,955,000	103,455,000	100,955,000	103,455,000			100,733,000
Estimated fair value of debt	100,955,000	103,455,000	100,955,000	103,455,000			100,733,000
5.875% Senior notes [Member]
Long-term debt [Abstract]
Senior unsecured notes annual interest rate (in hundredths)	5.875%		5.875%
Senior unsecured notes maturity date			Jun. 01, 2021
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	99,950,000	97,440,000	99,950,000	97,440,000			93,070,000
Estimated fair value of debt	99,950,000	97,440,000	99,950,000	97,440,000			93,070,000
0% Subordinated debentures [Member] | Level 2 [Member]
Long-term debt [Abstract]
Carrying Value	66,598,000	61,814,000	66,598,000	61,814,000			64,119,000
Fair Value Level 2	75,184,000	57,956,000	75,184,000	57,956,000			58,899,000
Senior unsecured notes annual interest rate (in hundredths)	0.00%		0.00%
Senior unsecured notes maturity date			Dec. 31, 2015
Estimated fair value of debt	$ 75,184,000	$ 57,956,000	$ 75,184,000	$ 57,956,000			$ 58,899,000