Gross Gains and Losses from Investment Sales (Details) - MSB - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Schedule Of Gain Loss On Investments Including Marketable Securities And Investments Held At Cost Income Statement Reported Amounts Summary [Line Items]
Gross gains	$ 5,894	$ 16,510
Gross losses	(1,607)	(57)
Net gain (loss)	$ 4,287	$ 16,453