Acquisitions (Narrative) (Details)			3 Months Ended		6 Months Ended
	Apr. 28, 2017 USD ($) entity	Mar. 10, 2017 USD ($) entity	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Short-term borrowings			$ 1,810,907,000		$ 1,810,907,000		$ 1,225,406,000
Long-term borrowings			407,876,000		407,876,000		436,280,000
Goodwill			740,265,000		740,265,000		621,193,000
Revenue			199,717,000	$ 164,969,000	381,408,000	$ 327,805,000
Professional Fees			10,353,000	7,712,000	21,629,000	15,333,000
Other expense			27,667,000	16,473,000	46,297,000	33,182,000
Loan expected to be uncollectible			221,865,000	$ 226,086,000	221,865,000	$ 226,086,000	$ 229,418,000	$ 181,179,000
Whitney Bank [Member]
Business Acquisition [Line Items]
Number of branches | entity		9
Net of cash acquired		$ 323,000,000
Cash consideration		326,000,000
Cash acquired		3,000,000
Acquisition, Premium amount to pay		41,600,000
FNBC Transaction [Member]
Business Acquisition [Line Items]
Acquisition, debt assumed			93,120,000		93,120,000
Identifiable intangible assets			24,400,000		24,400,000
Goodwill			119,072,000		119,072,000
Fair value discount					57,500,000
Acquisition, debt assumed			4,686,000		4,686,000
Total Loans			1,377,100,000		1,377,100,000
Unpaid principal balance of the loans acquired			1,400,000,000		1,400,000,000
Liabilities assumed			2,622,950,000		2,622,950,000
Estimated uncollectible amount			47,600,000		$ 47,600,000
FNBC I [Member]
Business Acquisition [Line Items]
Acquisition, debt assumed		93,120,000
Identifiable intangible assets		3,900,000
Goodwill		96,063,000
Acquisition, debt assumed		1,607,000
Goodwill adjustment			495,000
Total Loans		1,211,523,000
Useful life					8 years
Liabilities assumed		1,003,647,000
FNBC I [Member] | FHLB Borrowings [Member]
Business Acquisition [Line Items]
Liabilities assumed		$ 604,000,000
FNBC I [Member] | Variable-rate Term Notes [Member] | FHLB Borrowings [Member]
Business Acquisition [Line Items]
Short-term borrowings			460,000,000		$ 460,000,000
FNBC I [Member] | Fixed-rate Term Notes [Member] | FHLB Borrowings [Member]
Business Acquisition [Line Items]
Short-term borrowings			51,000,000		$ 51,000,000
Maturity year					2017
Long-term borrowings			93,100,000		$ 93,100,000
FNBC I [Member] | $200 Debt Due 2025 [Member] | Variable-rate Term Notes [Member] | FHLB Borrowings [Member]
Business Acquisition [Line Items]
Short-term borrowings			200,000,000		$ 200,000,000
Maturity year					2025
FNBC I [Member] | $260 Debt Due 2026 [Member] | Variable-rate Term Notes [Member] | FHLB Borrowings [Member]
Business Acquisition [Line Items]
Short-term borrowings			260,000,000		$ 260,000,000
Maturity year					2026
FNBC I [Member] | $88 Debt Due 2018 [Member] | Fixed-rate Term Notes [Member] | FHLB Borrowings [Member]
Business Acquisition [Line Items]
Maturity year					2018
Long-term borrowings			88,000,000		$ 88,000,000
FNBC I [Member] | $3.2 Debt Due 2019 [Member] | Fixed-rate Term Notes [Member] | FHLB Borrowings [Member]
Business Acquisition [Line Items]
Maturity year					2019
Long-term borrowings			3,200,000		$ 3,200,000
FNBC I [Member] | $1.9 Debt Due 2023 [Member] | Fixed-rate Term Notes [Member] | FHLB Borrowings [Member]
Business Acquisition [Line Items]
Maturity year					2023
Long-term borrowings			$ 1,900,000		$ 1,900,000
FNBC II [Member]
Business Acquisition [Line Items]
Identifiable intangible assets	$ 20,500,000
Goodwill	23,009,000
Acquisition, debt assumed	3,079,000
Total Loans	165,577,000
Useful life					9 years
Liabilities assumed	$ 1,619,303,000
FNBC II [Member] | Whitney Bank [Member]
Business Acquisition [Line Items]
Number of branches | entity	29
Cash received	$ 798,000,000
Cash acquired	158,000,000
Premium payment	35,000,000
Unpaid principal balance of the loans acquired	$ 640,000,000
FNBC II [Member] | Louisiana [Member] | Whitney Bank [Member]
Business Acquisition [Line Items]
Number of branches | entity	24
FNBC II [Member] | Florida [Member] | Whitney Bank [Member]
Business Acquisition [Line Items]
Number of branches | entity	5