Loans and Allowance - Changes in Allowance for Loan Losses by Loan Segment (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Allowance for loan losses:
Beginning balance	$ 63,964	$ 67,870
Provision for losses
Recoveries on loans	1,072	3,600
Loans charged off	(2,235)	(1,887)
Ending balance	62,801	69,583
Commercial
Allowance for loan losses:
Beginning balance	28,824	27,176
Provision for losses	1,834	2,387
Recoveries on loans	450	2,050
Loans charged off	(1,101)	(706)
Ending balance	30,007	30,907
Commercial Real Estate
Allowance for loan losses:
Beginning balance	19,327	23,102
Provision for losses	(2,896)	(1,257)
Recoveries on loans	412	790
Loans charged off	(460)	(277)
Ending balance	16,383	22,358
Consumer
Allowance for loan losses:
Beginning balance	2,658	2,515
Provision for losses	527	(12)
Recoveries on loans	78	136
Loans charged off	(125)	(229)
Ending balance	3,138	2,410
Residential
Allowance for loan losses:
Beginning balance	13,152	15,077
Provision for losses	534	(1,098)
Recoveries on loans	132	604
Loans charged off	(549)	(675)
Ending balance	13,269	13,908
Finance Leases
Allowance for loan losses:
Beginning balance	3
Provision for losses	1	(20)
Recoveries on loans		20
Loans charged off
Ending balance	$ 4