Loans and Allowance - Changes in Allowance for Loan Losses by Loan Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Allowance for loan losses:
Beginning balance	$ 62,550	$ 68,367	$ 63,964	$ 67,870
Provision for losses		1,600	417	1,600
Recoveries on loans	$ 2,371	3,722	4,875	8,527
Loans charged off	(2,060)	(8,093)	(6,395)	(12,401)
Ending balance	62,861	65,596	62,861	65,596
Commercial
Allowance for loan losses:
Beginning balance	31,479	28,614	28,824	27,176
Provision for losses	3,202	1,385	6,226	1,736
Recoveries on loans	281	1,987	1,168	4,485
Loans charged off	(1,026)	(4,444)	(2,282)	(5,855)
Ending balance	33,936	27,542	33,936	27,542
Commercial Real Estate
Allowance for loan losses:
Beginning balance	15,828	22,582	19,327	23,102
Provision for losses	(2,966)	528	(6,364)	(177)
Recoveries on loans	1,510	1,215	2,069	2,356
Loans charged off	(386)	(2,707)	(1,046)	(3,663)
Ending balance	13,986	21,618	13,986	21,618
Consumer
Allowance for loan losses:
Beginning balance	2,927	2,243	2,658	2,515
Provision for losses	(102)	113	225	(39)
Recoveries on loans	67	86	246	303
Loans charged off	(169)	(214)	(406)	(551)
Ending balance	2,723	2,228	2,723	2,228
Residential
Allowance for loan losses:
Beginning balance	12,311	14,928	13,152	15,077
Provision for losses	(132)	(424)	330	100
Recoveries on loans	513	431	1,392	1,360
Loans charged off	(479)	(728)	(2,661)	(2,330)
Ending balance	12,213	$ 14,207	12,213	$ 14,207
Finance Leases
Allowance for loan losses:
Beginning balance	5		$ 3
Provision for losses	$ (2)	$ (2)		$ (20)
Recoveries on loans		$ 3		23
Loans charged off				(2)
Ending balance	$ 3	$ 1	$ 3	$ 1