Loans, Changes in the Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Change in the allowance for unfunded commitments
Balance at beginning of period	$ 24,000
Balance at end of period	26,000	$ 24,000
Allowance for Unfunded Commitments:
Change in the allowance for unfunded commitments
Balance at beginning of period	24,400	25,400
Provision for unfunded commitments	(500)	(1,000)
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Provision for Loan Losses	2,436	0
Balance at end of period	$ 26,336	$ 24,400