Allowance for Loan Losses - Loan Status and Aging of Past Due TDR Loans (Details) - Troubled Debt Restructured Loans - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR loans in in-school/grace/deferment	$ 10,738	$ 6,869
TDR loans in forbearance	42,699	43,756
TDR loans in repayment and percentage of each status:
Loans current	232,720	185,936
Total TDR loans in repayment	264,657	215,206
Total TDR loans, gross	$ 318,094	$ 265,831
Loans current, in percentage	88.00%	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	$ 13,610	$ 14,948
Loans delinquent, in percentage	5.10%	6.90%
Loans delinquent 61-90 days
TDR loans in repayment and percentage of each status:
Loans delinquent	$ 11,109	$ 9,239
Loans delinquent, in percentage	4.20%	4.30%
Loans delinquent greater than 90 days
TDR loans in repayment and percentage of each status:
Loans delinquent	$ 7,218	$ 5,083
Loans delinquent, in percentage	2.70%	2.40%