Internal Risk Rating Categories for Commercial Portfolio (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	$ 4,874,718	$ 4,539,256
Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	1,093,629	888,528
Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	3,251,248	3,116,561
Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	365,165	401,797
Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	164,676	132,370
Pass [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	4,695,094	4,345,232
Pass [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	1,014,370	806,331
Pass [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	3,156,989	3,007,672
Pass [Member] | Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	361,884	400,964
Pass [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	161,851	130,265
Potential weakness [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	74,886	87,822
Potential weakness [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	16,860	16,563
Potential weakness [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	56,840	69,788
Potential weakness [Member] | Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	298	0
Potential weakness [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	888	1,471
Definite weakness [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	101,248	99,516
Definite weakness [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	58,909	59,415
Definite weakness [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	37,419	38,637
Definite weakness [Member] | Construction Loans [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	2,983	833
Definite weakness [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	1,937	631
Parital loss probable [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	3,490	6,686
Parital loss probable [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	3,490	6,219
Parital loss probable [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
Financing Receivable, Net	0	464
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	0	3
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