Investment Securities - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Investment Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sale of available-for-sale investment securities	$ 8,700	$ 39,700	$ 83,735	$ 770,149
Available-for-sale Securities, Gross Realized Losses	0	500	0	800
Available-for-sale Securities, Gross Realized Gains	$ 100	$ 100	$ 100	$ 600
Floating rate auction-rate certificates backed by Government guaranteed student loans
Schedule of Available-for-sale Securities [Line Items]
Other-Than-Temporary Impairment Loss Sales Price, As Percent of Par	99.63%		99.63%
Floating Interest Rate [Member] | Floating rate auction-rate certificates backed by Government guaranteed student loans
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments	$ 100		$ 100