Loans and Allowance - Changes in Allowance for Loan Losses by Loan Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Allowance for loan losses:
Beginning balance				$ 63,964				$ 67,870	$ 63,964	$ 67,870	$ 69,366
Provision for losses			$ 417		$ 960	$ 1,600			417	2,560	6,648
Recoveries on loans									6,344	10,916	9,990
Loans charged off									(8,272)	(17,382)	(18,134)
Ending balance	$ 62,453				63,964				62,453	63,964	67,870
Commercial
Allowance for loan losses:
Beginning balance				$ 28,824				$ 27,176	28,824	27,176	25,913
Provision for losses									(1,901)	3,459	2,794
Recoveries on loans									1,911	5,435	4,586
Loans charged off									(2,356)	(7,246)	(6,117)
Ending balance	26,478				28,824				26,478	28,824	27,176
Commercial Real Estate
Allowance for loan losses:
Beginning balance				19,327				23,102	19,327	23,102	26,703
Provision for losses									1,710	(464)	340
Recoveries on loans									2,545	3,297	3,552
Loans charged off									(1,437)	(6,608)	(7,493)
Ending balance	22,145				19,327				22,145	19,327	23,102
Consumer
Allowance for loan losses:
Beginning balance				2,658				2,515	2,658	2,515	2,593
Provision for losses									299	423	(11)
Recoveries on loans									352	377	556
Loans charged off									(620)	(657)	(623)
Ending balance	2,689				2,658				2,689	2,658	2,515
Residential
Allowance for loan losses:
Beginning balance				13,152				$ 15,077	13,152	15,077	14,157
Provision for losses									310	(839)	3,514
Recoveries on loans									1,536	1,783	1,292
Loans charged off									(3,859)	(2,869)	(3,886)
Ending balance	11,139				13,152				11,139	$ 13,152	$ 15,077
Finance Leases
Allowance for loan losses:
Beginning balance				$ 3					3
Provision for losses									$ (1)	$ (19)	$ 11
Recoveries on loans										24	4
Loans charged off										(2)	$ (15)
Ending balance	$ 2				$ 3				$ 2	$ 3