Previously Consolidated Variable Interest Entities (Details 3) (Previously Consolidated Variable Interest Entities, USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Less than 12 months, Estimated Fair Value	$ 155,200
Less than 12 months, Gross Unrealized Losses	(4,700)
Greater than 12 months , Estimated Fair Value	130,300
Greater than 12 months , Gross Unrealized Losses	(12,200)
Total, Estimated Fair Value	285,500
Total Gross Unrealized Losses	(16,900)
[HeldToMaturitySecuritiesExcluded]	302,400	[1]
Floating Rate
Less than 12 months, Estimated Fair Value
Less than 12 months, Gross Unrealized Losses
Greater than 12 months , Estimated Fair Value	200
Greater than 12 months , Gross Unrealized Losses	(1,100)
Total, Estimated Fair Value	200
Total Gross Unrealized Losses	(1,100)
[HeldToMaturitySecuritiesExcluded]	1,300	[1]
Fixed Rate
Less than 12 months, Estimated Fair Value	155,200
Less than 12 months, Gross Unrealized Losses	(4,700)
Greater than 12 months , Estimated Fair Value	130,100
Greater than 12 months , Gross Unrealized Losses	(11,100)
Total, Estimated Fair Value	285,300
Total Gross Unrealized Losses	(15,800)
[HeldToMaturitySecuritiesExcluded]	$ 301,100	[1]

[1] Excludes, as of December 31, 2011, $59.2 million of securities which were carried at or below fair value and securities against which an other-than-temporary impairment equal to the entire book value was recognized in earnings.