Allowance for Loan Losses - Modified Loan Accounts for TDR (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Receivables [Abstract]
Modified Loans	$ 498,812	$ 398,324	$ 244,890
Charge-offs	48,469	24,628	10,877
Payment-Default	$ 92,532	$ 64,811	$ 51,602