Internal Risk Rating Categories for Commercial Portfolio (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	$ 4,355,968	$ 3,966,324
Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	902,053	843,276
Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	3,010,798	2,653,434
Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	320,391	373,368
Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	122,726	96,246
Pass [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	4,097,798	3,706,567
Pass [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	783,825	765,753
Pass [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	2,876,570	2,484,025
Pass [Member] | Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	317,099	363,781
Pass [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	120,304	93,008
Potential weakness [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	134,039	176,519
Potential weakness [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	46,176	54,375
Potential weakness [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	84,641	112,022
Potential weakness [Member] | Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	1,363	7,678
Potential weakness [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	1,859	2,444
Definite weakness [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	121,640	81,990
Definite weakness [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	71,991	23,073
Definite weakness [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	47,164	56,276
Definite weakness [Member] | Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	1,929	1,909
Definite weakness [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	556	732
Parital loss probable [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	2,491	1,248
Parital loss probable [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	61	75
Parital loss probable [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	2,423	1,111
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	7	62
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