Federal Home Loan Bank Advances and Other Borrowings (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) bank	Dec. 31, 2014 USD ($)
Federal Home Loan Bank Advances and Other Borrowings
Maximum percentage of assets up to which advances will be provided by FHLB	45.00%
Maximum credit line available from FHLB	$ 1,200,000,000
Overnight FHLB advances	98,000,000	$ 20,000,000
FHLB advances	148,000,000	70,000,000
Maximum amount outstanding in respect of term advances	50,000,000	50,000,000
Aggregate principal balance of real estate loans used to collateralize FHLB advances	620,000,000
Federal Home Loan Bank Stock	11,400,000
Additional available advances	385,000,000
Estimated fair value of MBS used to secure outstanding borrowings	34,000,000	$ 50,000,000
Securities Sold under Agreements to Repurchase	$ 28,500,000
Weighted average rate for securities sold under agreement to repurchase (as a percent)	0.39%	0.26%
Credit facilities | Citigroup
Federal Home Loan Bank Advances and Other Borrowings
Balance outstanding at end of year	$ 18,500,000	$ 18,500,000
Credit facilities | Barclays Bank
Federal Home Loan Bank Advances and Other Borrowings
Balance outstanding at end of year	10,000,000	10,000,000
Reverse repurchase facility
Federal Home Loan Bank Advances and Other Borrowings
Estimated fair value of MBS used to secure outstanding borrowings	19,600,000
Securities Sold under Agreements to Repurchase	$ 28,500,000
Weighted average rate for securities sold under agreement to repurchase (as a percent)	0.03%
Reverse repurchase facility | Union Bank
Federal Home Loan Bank Advances and Other Borrowings
Unused facility	$ 50,000,000
Unsecured lines of credit
Federal Home Loan Bank Advances and Other Borrowings
Unused facility	$ 120,000,000
Number of correspondent banks | bank	7
Amount outstanding	$ 0	$ 1,500,000
Federal Reserve discount window
Federal Home Loan Bank Advances and Other Borrowings
Unused facility	$ 3,300,000