Investments (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Net change in unrealized gains (losses) from other trading account assets	$ 300,000	$ 200,000	$ 700,000	$ (300,000)
Net investment income	51,321,000	71,371,000	168,794,000	214,441,000
Gross unrealized losses related to high or highest quality securities	22,100,000		22,100,000		1,600,000
Gross unrealized losses related to other than high or highest quality securities	1,900,000		1,900,000		300,000
Gross unrealized losses representing declines in value of greater than 20%	0		0		0
Gross unrealized losses in a continuous loss position for less than six months	0		0		0
Twelve months or more Unrealized Losses	$ 1,988,000		$ 1,988,000		$ 620,000