Debt (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) DebentureRepurchased $ / shares	Sep. 30, 2014 USD ($) DebentureRepurchased	Sep. 30, 2015 USD ($) DebentureRepurchased $ / shares	Sep. 30, 2014 USD ($) DebentureRepurchased	Dec. 31, 2014 USD ($)
Long-term debt [Abstract]
Carrying Value	$ 106,750,000	$ 111,941,000	$ 106,750,000	$ 111,941,000	$ 112,163,000
Fair Value Level 2	113,425,000	120,975,000	113,425,000	120,975,000	123,123,000
Loss on extinguishment of debt			(310,000)	(84,000)
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	$ 106,625,000	$ 108,200,000	106,625,000	$ 108,200,000	$ 110,123,000
0% Subordinated debentures [Member]
Long-term debt [Abstract]
Carrying Value	$ 6,750,000	$ 11,941,000	$ 6,750,000	$ 11,941,000	$ 12,163,000
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)	$ 1,600	$ 100,000	$ 6,200,000	$ 700,000
Debentures repurchased (loss in dollars)	$ 1,000	$ 10,000	310,000	$ 84,000
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) | $ / shares	$ 3.20
Par value of debentures | $ / shares	$ 100		$ 100
Debt redemption price as percentage of principal amount (in hundredths)	100.00%		100.00%
Number of debentures repurchased | DebentureRepurchased	16	1,032	62,242	7,165
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	500,000,000		500,000,000
0% Subordinated debentures [Member] | Level 2 [Member]
Long-term debt [Abstract]
Fair Value Level 2	$ 6,800,000	$ 12,775,000	$ 6,800,000	$ 12,775,000	$ 13,000,000