Investment Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	$ 19,471	$ 5,020	$ 7,210
Twelve Months or More	12,005	7,797	362
Securities Available for Sale, Fair Value
Less Than Twelve Months	1,042,754	654,893	700,546
Twelve Months or More	360,489	374,582	3,391
Government-sponsored entities debt
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	918	403	721
Twelve Months or More	819	674
Securities Available for Sale, Fair Value
Less Than Twelve Months	34,712	27,442	87,609
Twelve Months or More	55,034	52,324
State and municipal obligations
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	1,523	124	140
Twelve Months or More	17
Securities Available for Sale, Fair Value
Less Than Twelve Months	69,118	17,400	10,984
Twelve Months or More	724
Mortgage-backed securities. issued by Government sponsored entities
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	17,030	4,493	6,349
Twelve Months or More	11,169	7,123	71
Securities Available for Sale, Fair Value
Less Than Twelve Months	938,924	610,051	601,953
Twelve Months or More	$ 304,731	$ 322,258	1,940
Corporate securities
Securities Available for Sale, Gross Unrealized Losses
Twelve Months or More			291
Securities Available for Sale, Fair Value
Twelve Months or More			$ 1,451