Allowance for Loan Losses - Loan Status and Aging of Past Due TDR Loans (Details) - Troubled Debt Restructured Loans - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR loans in in-school/grace/deferment	$ 4,940	$ 2,915
TDR loans in forbearance	50,878	18,620
TDR loans in repayment and percentage of each status:
Loans current	154,984	34,554
Total TDR loans in repayment	175,468	37,867
Total TDR loans, gross	$ 231,286	$ 59,402
Loans current, in percentage	88.30%	91.20%
Total TDR loans in repayment, in percentage	100.00%	100.00%
Loans delinquent 31-60 days
TDR loans in repayment and percentage of each status:
Loans delinquent	$ 11,042	$ 1,953
Loans delinquent, in percentage	6.30%	5.20%
Loans delinquent 61-90 days
TDR loans in repayment and percentage of each status:
Loans delinquent	$ 6,336	$ 983
Loans delinquent, in percentage	3.60%	2.60%
Loans delinquent greater than 90 days
TDR loans in repayment and percentage of each status:
Loans delinquent	$ 3,106	$ 377
Loans delinquent, in percentage	1.80%	1.00%