Debt (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014 DebentureRepurchased	Jun. 30, 2013 DebentureRepurchased	Jun. 30, 2014 DebentureRepurchased	Jun. 30, 2013 DebentureRepurchased	Dec. 31, 2013
Long-term debt [Abstract]
Carrying Value	$ 111,813,000	$ 117,028,000	$ 111,813,000	$ 117,028,000	$ 111,911,000
Fair Value Level 2	121,727,000	123,049,000	121,727,000	123,049,000	122,319,000
Loss on extinguishment of debt			(74,000)	(137,000)
5.5% Senior notes [Member]
Long-term debt [Abstract]
Debt maturity date	May 15, 2013
Stated interest rate (in hundredths)	5.50%	5.50%	5.50%	5.50%	5.50%
Debt maturity period	10 years
Face value of debt	100,000,000		100,000,000
5.875% Senior notes [Member]
Long-term debt [Abstract]
Carrying Value	100,000,000	100,000,000	100,000,000	100,000,000	100,000,000
Debt maturity date	Jun. 01, 2021
Stated interest rate (in hundredths)	5.875%	5.875%	5.875%	5.875%	5.875%
Debt maturity period	10 years
Face value of debt	100,000,000		100,000,000
Percentage principal amount to offered to repurchase notes (in hundredths)	101.00%
5.875% Senior notes [Member] | Level 2 [Member]
Long-term debt [Abstract]
Fair Value Level 2	108,521,000	104,125,000	108,521,000	104,125,000	108,500,000
0% Subordinated debentures [Member]
Long-term debt [Abstract]
Carrying Value	11,813,000	17,028,000	11,813,000	17,028,000	11,911,000
Debt maturity date	Dec. 31, 2015
Stated interest rate (in hundredths)	0.00%	0.00%	0.00%	0.00%	0.00%
Effective interest rate (in hundredths)	7.45%	7.45%	7.45%	7.45%	7.45%
Debentures repurchased (face value)	572,000	1,200,000	613,000	1,200,000
Debentures repurchased (loss in dollars)	69,000	137,000	74,000	137,000
Debt maturity period	5 years
Face value of debt	86,400,000		86,400,000
Dividends declared related to issuance of debt (in dollars per share)	$ 3.20
Par value of debentures	100,000,000		100,000,000
Debt redemption price as percentage of principal amount (in hundredths)	100.00%		100.00%
Number of debentures repurchased	5,717	11,942	6,133	11,974
Maximum amount of debt and equity to be issued under Shelf Registration	500,000,000		500,000,000
Amount available for debt and equity issuance under Shelf Registration	400,000,000		400,000,000
0% Subordinated debentures [Member] | Level 2 [Member]
Long-term debt [Abstract]
Fair Value Level 2	$ 13,206,000	$ 18,924,000	$ 13,206,000	$ 18,924,000	$ 13,819,000