Investment Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	$ 24,290	$ 5,020	$ 5,921
Twelve Months or More	14,324	7,797	508
Securities Available for Sale, Fair Value
Less Than Twelve Months	1,062,660	654,893	650,022
Twelve Months or More	341,687	374,582	15,187
Government-sponsored entities debt
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	1,179	403	608
Twelve Months or More	141	674
Securities Available for Sale, Fair Value
Less Than Twelve Months	39,145	27,442	70,226
Twelve Months or More	8,468	52,324
State and municipal obligations
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	1,617	124	106
Twelve Months or More	32
Securities Available for Sale, Fair Value
Less Than Twelve Months	77,373	17,400	9,171
Twelve Months or More	1,348
Mortgage-backed securities. issued by Government sponsored entities
Securities Available for Sale, Gross Unrealized Losses
Less Than Twelve Months	21,494	4,493	5,207
Twelve Months or More	14,151	7,123	109
Securities Available for Sale, Fair Value
Less Than Twelve Months	946,142	610,051	570,625
Twelve Months or More	$ 331,871	$ 322,258	13,854
Corporate securities
Securities Available for Sale, Gross Unrealized Losses
Twelve Months or More			399
Securities Available for Sale, Fair Value
Twelve Months or More			$ 1,333