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, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR loans in in-school/grace/deferment	$ 22,544	$ 6,869
TDR loans in forbearance	72,386	43,756
TDR loans in repayment and percentage of each status:
Loans current	366,000	185,936
Total TDR loans in repayment	408,702	215,206
Total TDR loans, gross	$ 503,632	$ 265,831
Loans current (as a percentage)	89.60%	86.40%
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	$ 21,781	$ 14,948
Loans delinquent (as a percentage)	5.30%	6.90%
Loans delinquent 61-90 days
TDR loans in repayment and percentage of each status:
Loans delinquent	$ 13,411	$ 9,239
Loans delinquent (as a percentage)	3.30%	4.30%
Loans delinquent greater than 90 days
TDR loans in repayment and percentage of each status:
Loans delinquent	$ 7,510	$ 5,083
Loans delinquent (as a percentage)	1.80%	2.40%