Loans, Allowance for Loan Losses and Credit Quality (Internal Risk-Rating Categories for the Commercial Portfolio) (Details) $ in Thousands	Dec. 31, 2019 USD ($)
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	$ 6,119,185
Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,395,036
Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	4,002,359
Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	547,293
Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	174,497
PASS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	5,848,531
PASS [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,274,155
PASS [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	3,860,555
PASS [Member] | Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	542,608
PASS [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	171,213
POTENTIAL WEAKNESS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	164,416
POTENTIAL WEAKNESS [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	63,485
POTENTIAL WEAKNESS [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	97,268
POTENTIAL WEAKNESS [Member] | Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,247
POTENTIAL WEAKNESS [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,416
DEFINITE WEAKNESS-LOSS UNLIKELY [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	106,238
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	57,396
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	44,536
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	2,438
DEFINITE WEAKNESS-LOSS UNLIKELY [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	1,868
PARTIAL LOSS PROBABLE [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	0
PARTIAL LOSS PROBABLE [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	0
PARTIAL LOSS PROBABLE [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	0
PARTIAL LOSS PROBABLE [Member] | Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	0
PARTIAL LOSS PROBABLE [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	0
DEFINITE LOSS [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	0
DEFINITE LOSS [Member] | Commercial and Industrial [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	0
DEFINITE LOSS [Member] | Commercial Real Estate [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	0
DEFINITE LOSS [Member] | Commercial Construction [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	0
DEFINITE LOSS [Member] | Small Business [Member]
Internal risk-rating categories for the Company's commercial portfolio
TOTAL	$ 0