Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Maximum refinement period of fair values after closing date of acquisition	1 year
Loan minimum balance included in specific reseve analysis	$ 1,000
Tax credit carry forward period	20 years
Income tax benefit	$ 92,802	$ 37,627	$ 38,304
Reclassification of certain tax effects from accumulated other comprehensive loss
Accounting Standards Update 2016-09 [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Income tax benefit	$ (5,800)
Federal NMTC Investment [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Tax credit earning period	7 years
State NMTC Investment [Member] | Minimum [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Tax credit earning period	3 years
State NMTC Investment [Member] | Maximum [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Tax credit earning period	5 years
Low Income Housing Credit Investments [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Tax credit earning period	10 years
Buildings [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Estimated useful lives of assets	30 years
Furniture, Fixtures and Equipment [Member] | Minimum [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Estimated useful lives of assets	3 years
Furniture, Fixtures and Equipment [Member] | Maximum [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Estimated useful lives of assets	10 years
Software [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Amortization Expense Charged Off Period	3 years
Core Systems [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Amortization Expense Charged Off Period	7 years
Commercial Loans [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Loss emergence periods	24 months
Retail Loans [Member] | Minimum [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Loss emergence periods	12 months
Residential Mortgages Loans [Member] | Maximum [Member]
Summary Of Significant Accounting Policies And Recent Accounting Pronouncements [Line Items]
Loss emergence periods	18 months