Allowance for Credit Losses - Allocation of Allowance for Loan Losses and Related Loans by Segment (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	$ 23,234,716	$ 18,331,580
Allowance for loan losses
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	28,508	14,561
Collectively evaluated for impairment	110,254	106,295
Total Loans	138,762	120,856
Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	156,191	164,166
Collectively evaluated for impairment	18,430,824	16,780,199
Loans \| Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	4,647,701	1,387,215
Commercial and Industrial
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	3,829,525	2,741,425
Commercial and Industrial \| Allowance for loan losses
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	24,817	11,044
Collectively evaluated for impairment	49,440	46,188
Total Loans	74,257	57,232
Commercial and Industrial \| Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	87,170	85,499
Collectively evaluated for impairment	2,934,354	2,463,566
Commercial and Industrial \| Loans \| Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	808,001	192,360
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	13,290,562	10,347,882
Commercial Real Estate \| Allowance for loan losses
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	2,987	2,735
Collectively evaluated for impairment	50,825	52,219
Total Loans	53,812	54,954
Commercial Real Estate \| Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	54,719	60,851
Collectively evaluated for impairment	10,051,628	9,310,964
Commercial Real Estate \| Loans \| Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	3,184,215	976,067
Residential Mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	3,528,682	2,859,035
Residential Mortgage \| Allowance for loan losses
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	632	718
Collectively evaluated for impairment	3,992	2,887
Total Loans	4,624	3,605
Residential Mortgage \| Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	12,849	14,056
Collectively evaluated for impairment	3,038,580	2,703,688
Residential Mortgage \| Loans \| Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	477,253	141,291
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	2,585,947	2,383,238
Consumer \| Allowance for loan losses
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	72	64
Collectively evaluated for impairment	5,997	5,001
Total Loans	6,069	5,065
Consumer \| Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	1,453	3,760
Collectively evaluated for impairment	2,406,262	2,301,981
Consumer \| Loans \| Loans acquired with discounts related to credit quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Loans	$ 178,232	$ 77,497

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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The balance of financing receivables that were individually evaluated for impairment.

+ References

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- Definition

Amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date. Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. Excludes amounts related to receivables held-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10(3))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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