Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Time certificates of deposit least amount	$ 100,000	$ 100,000
Securities held to maturity, fair value	$ 494,194,000	$ 485,650,000
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	75,000,000	75,000,000
Common stock, shares issued	27,450,190	27,005,813
Common stock, unvested restricted Stock awards	177,191	212,698
Shares held in rabbit trust at cost	164,438	170,036
Common Stock Outstanding
Common stock, shares outstanding	27,450,190	27,005,813
Junior Subordinated Debt [Member]
Unamortized Debt Issuance Expense	$ 125,000,000	$ 136,000,000
Subordinated Debt [Member]
Unamortized Debt Issuance Expense	$ 318,000,000	$ 365,000