Internal Risk Rating Categories for Commercial Portfolio (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	$ 3,966,324	$ 3,559,403
Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	843,276	860,839
Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	2,653,434	2,347,323
Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	373,368	265,994
Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	96,246	85,247
Pass [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	3,706,567	3,327,638
Pass [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	765,753	801,578
Pass [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	2,484,025	2,196,109
Pass [Member] | Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	363,781	248,696
Pass [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	93,008	81,255
Potential weakness [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	176,519	138,570
Potential weakness [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	54,375	37,802
Potential weakness [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	112,022	82,372
Potential weakness [Member] | Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	7,678	15,464
Potential weakness [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	2,444	2,932
Definite weakness [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	81,990	90,595
Definite weakness [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	23,073	20,241
Definite weakness [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	56,276	67,571
Definite weakness [Member] | Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	1,909	1,834
Definite weakness [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	732	949
Parital loss probable [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	1,248	2,600
Parital loss probable [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	75	1,218
Parital loss probable [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	1,111	1,271
Parital loss probable [Member] | Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	0	0
Parital loss probable [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	62	111
Definite loss [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	0	0
Definite loss [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	0	0
Definite loss [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	0	0
Definite loss [Member] | Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	0	0
Definite loss [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	$ 0	$ 0