Subsequent Events (Details 1) $ / shares in Units, $ in Thousands			3 Months Ended			9 Months Ended
	Nov. 02, 2015 $ / shares	Oct. 06, 2015 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares	Jun. 30, 2015 $ / shares	Sep. 30, 2014 $ / shares	Sep. 30, 2015 USD ($) bank_branch $ / shares	Sep. 30, 2014 $ / shares	Dec. 31, 2014 USD ($) $ / shares
Subsequent Event [Line Items]
Common Stock par value (usd per share) | $ / shares			$ 0.01			$ 0.01		$ 0.01
Assets			$ 16,814,105			$ 16,814,105		$ 16,234,605
Dividends declared per share (usd per share) | $ / shares			$ 0.5	$ 0.5	$ 0.25	$ 1.50	$ 0.75
Subsequent Event, Description						0
Subsequent Event [Member]
Subsequent Event [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage		15.00%
Assets		$ 4,000,000
Dividends Payable, Date Declared	Nov. 02, 2015
Dividends Payable, Date to be Paid	Nov. 30, 2015
Dividends Payable, Date of Record	Nov. 16, 2015
Dividend Declared [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends declared per share (usd per share) | $ / shares	$ 0.5
Square 1 Financial, Inc. [Member]
Subsequent Event [Line Items]
Assets			$ 21,000,000			$ 21,000,000
Retail Branch Locations | bank_branch						80
Business Combinations, Acquired Locations | bank_branch						1
Square 1 Financial, Inc. [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Business Acquisition, Effective Date of Acquisition		Oct. 06, 2015
Common Stock par value (usd per share) | $ / shares		$ 43.97
Total consideration paid		$ 815,000
Business Acquisition Shares Receivable By Stockholders Of Acquiree Ratio | shares		0.5597
Common Stock, Value, Outstanding		$ 17,800
Shares Of Common Stock [Member] | Square 1 Financial, Inc. [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Stock Issued During Period, Shares, New Issues | shares		18,100,000