Loans and Allowance for Credit Losses - Risk category of loans by class of loans (Details 10) - Loans Receivable - USD ($) $ in Thousands		Jun. 30, 2016	Dec. 31, 2015
Risk category of loans by class of loans
Total loans, excluding PCI loans		$ 6,245,793	$ 5,944,122
Loans Outstanding, PCI		40,734	51,319
Pass
Risk category of loans by class of loans
Total loans, excluding PCI loans		6,079,910	5,770,315
Loans Outstanding, PCI		10,839	13,464
Watch
Risk category of loans by class of loans
Total loans, excluding PCI loans	[1]	44,073	48,473
Loans Outstanding, PCI	[1]	11,841	13,009
Substandard
Risk category of loans by class of loans
Total loans, excluding PCI loans		121,810	125,334
Loans Outstanding, PCI		18,054	23,935
Doubtful / Loss
Risk category of loans by class of loans
Total loans, excluding PCI loans
Loans Outstanding, PCI			911
Home equity lines of credit
Risk category of loans by class of loans
Total loans, excluding PCI loans		621,626	596,118
Loans Outstanding, PCI		1,178	1,688
Home equity lines of credit | Pass
Risk category of loans by class of loans
Total loans, excluding PCI loans		615,840	589,749
Loans Outstanding, PCI		205	214
Home equity lines of credit | Watch
Risk category of loans by class of loans
Total loans, excluding PCI loans	[1]	21	24
Loans Outstanding, PCI	[1]
Home equity lines of credit | Substandard
Risk category of loans by class of loans
Total loans, excluding PCI loans		5,765	6,345
Loans Outstanding, PCI		973	1,474
Home equity lines of credit | Doubtful / Loss
Risk category of loans by class of loans
Total loans, excluding PCI loans
Loans Outstanding, PCI
Indirect auto
Risk category of loans by class of loans
Total loans, excluding PCI loans		475,116	455,922
Loans Outstanding, PCI		22	49
Indirect auto | Pass
Risk category of loans by class of loans
Total loans, excluding PCI loans		472,792	453,935
Loans Outstanding, PCI
Indirect auto | Watch
Risk category of loans by class of loans
Total loans, excluding PCI loans	[1]
Loans Outstanding, PCI	[1]
Indirect auto | Substandard
Risk category of loans by class of loans
Total loans, excluding PCI loans		2,324	1,987
Loans Outstanding, PCI		22	49
Indirect auto | Doubtful / Loss
Risk category of loans by class of loans
Total loans, excluding PCI loans
Loans Outstanding, PCI
Commercial
Risk category of loans by class of loans
Total loans, excluding PCI loans		3,642,337	3,400,948
Loans Outstanding, PCI		35,837	44,242
Commercial | Pass
Risk category of loans by class of loans
Total loans, excluding PCI loans		3,546,193	3,292,003
Loans Outstanding, PCI		10,106	12,904
Commercial | Watch
Risk category of loans by class of loans
Total loans, excluding PCI loans	[1]	30,045	39,566
Loans Outstanding, PCI	[1]	11,455	12,560
Commercial | Substandard
Risk category of loans by class of loans
Total loans, excluding PCI loans		66,099	69,379
Loans Outstanding, PCI		14,276	18,379
Commercial | Doubtful / Loss
Risk category of loans by class of loans
Total loans, excluding PCI loans
Loans Outstanding, PCI			399
Commercial | Owner occupied commercial real estate
Risk category of loans by class of loans
Total loans, excluding PCI loans		1,441,736	1,480,292
Loans Outstanding, PCI		8,339	13,674
Commercial | Owner occupied commercial real estate | Pass
Risk category of loans by class of loans
Total loans, excluding PCI loans		1,386,558	1,414,353
Loans Outstanding, PCI		1,399	1,811
Commercial | Owner occupied commercial real estate | Watch
Risk category of loans by class of loans
Total loans, excluding PCI loans	[1]	19,766	24,175
Loans Outstanding, PCI	[1]	2,842	6,705
Commercial | Owner occupied commercial real estate | Substandard
Risk category of loans by class of loans
Total loans, excluding PCI loans		35,412	41,764
Loans Outstanding, PCI		4,098	4,809
Commercial | Owner occupied commercial real estate | Doubtful / Loss
Risk category of loans by class of loans
Total loans, excluding PCI loans
Loans Outstanding, PCI			349
Commercial | Income producing commercial real estate
Risk category of loans by class of loans
Total loans, excluding PCI loans		897,563	795,958
Loans Outstanding, PCI		21,400	27,771
Commercial | Income producing commercial real estate | Pass
Risk category of loans by class of loans
Total loans, excluding PCI loans		872,759	771,792
Loans Outstanding, PCI		6,885	9,378
Commercial | Income producing commercial real estate | Watch
Risk category of loans by class of loans
Total loans, excluding PCI loans	[1]	5,027	4,151
Loans Outstanding, PCI	[1]	5,644	5,766
Commercial | Income producing commercial real estate | Substandard
Risk category of loans by class of loans
Total loans, excluding PCI loans		19,777	20,015
Loans Outstanding, PCI		8,871	12,627
Commercial | Income producing commercial real estate | Doubtful / Loss
Risk category of loans by class of loans
Total loans, excluding PCI loans
Loans Outstanding, PCI
Commercial | Construction
Risk category of loans by class of loans
Total loans, excluding PCI loans		378,610	339,936
Loans Outstanding, PCI		4,948	2,142
Commercial | Construction | Pass
Risk category of loans by class of loans
Total loans, excluding PCI loans		375,061	335,571
Loans Outstanding, PCI		1,619	1,698
Commercial | Construction | Watch
Risk category of loans by class of loans
Total loans, excluding PCI loans	[1]	2,043	3,069
Loans Outstanding, PCI	[1]	2,945	6
Commercial | Construction | Substandard
Risk category of loans by class of loans
Total loans, excluding PCI loans		1,506	1,296
Loans Outstanding, PCI		384	438
Commercial | Construction | Doubtful / Loss
Risk category of loans by class of loans
Total loans, excluding PCI loans
Loans Outstanding, PCI
Commercial | Commercial & industrial
Risk category of loans by class of loans
Total loans, excluding PCI loans		924,428	784,762
Loans Outstanding, PCI		1,150	655
Commercial | Commercial & industrial | Pass
Risk category of loans by class of loans
Total loans, excluding PCI loans		911,815	770,287
Loans Outstanding, PCI		203	17
Commercial | Commercial & industrial | Watch
Risk category of loans by class of loans
Total loans, excluding PCI loans	[1]	3,209	8,171
Loans Outstanding, PCI	[1]	24	83
Commercial | Commercial & industrial | Substandard
Risk category of loans by class of loans
Total loans, excluding PCI loans		9,404	6,304
Loans Outstanding, PCI		923	505
Commercial | Commercial & industrial | Doubtful / Loss
Risk category of loans by class of loans
Total loans, excluding PCI loans
Loans Outstanding, PCI			50
Residential | Residential mortgage
Risk category of loans by class of loans
Total loans, excluding PCI loans		1,032,256	1,025,487
Loans Outstanding, PCI		3,211	4,176
Residential | Residential mortgage | Pass
Risk category of loans by class of loans
Total loans, excluding PCI loans		986,571	985,109
Loans Outstanding, PCI		193
Residential | Residential mortgage | Watch
Risk category of loans by class of loans
Total loans, excluding PCI loans	[1]	7,652	5,070
Loans Outstanding, PCI	[1]	359	410
Residential | Residential mortgage | Substandard
Risk category of loans by class of loans
Total loans, excluding PCI loans		38,033	35,308
Loans Outstanding, PCI		2,659	3,766
Residential | Residential mortgage | Doubtful / Loss
Risk category of loans by class of loans
Total loans, excluding PCI loans
Loans Outstanding, PCI
Residential | Construction
Risk category of loans by class of loans
Total loans, excluding PCI loans		350,399	350,577
Loans Outstanding, PCI		478	1,123
Residential | Construction | Pass
Risk category of loans by class of loans
Total loans, excluding PCI loans		335,266	335,341
Loans Outstanding, PCI		334	345
Residential | Construction | Watch
Risk category of loans by class of loans
Total loans, excluding PCI loans	[1]	6,355	3,813
Loans Outstanding, PCI	[1]	27	39
Residential | Construction | Substandard
Risk category of loans by class of loans
Total loans, excluding PCI loans		8,778	11,423
Loans Outstanding, PCI		117	227
Residential | Construction | Doubtful / Loss
Risk category of loans by class of loans
Total loans, excluding PCI loans
Loans Outstanding, PCI			512
Consumer installment
Risk category of loans by class of loans
Total loans, excluding PCI loans		124,059	115,070
Loans Outstanding, PCI		8	41
Consumer installment | Pass
Risk category of loans by class of loans
Total loans, excluding PCI loans		123,248	114,178
Loans Outstanding, PCI		1	1
Consumer installment | Watch
Risk category of loans by class of loans
Total loans, excluding PCI loans	[1]
Loans Outstanding, PCI	[1]
Consumer installment | Substandard
Risk category of loans by class of loans
Total loans, excluding PCI loans		811	892
Loans Outstanding, PCI		7	40
Consumer installment | Doubtful / Loss
Risk category of loans by class of loans
Total loans, excluding PCI loans
Loans Outstanding, PCI

[1] Residential mortgage loans and home equity loans reported in the watch column are generally commercial purpose loans secured by the borrower's residence.