Investment Securities (Held to Maturity) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 466,945	$ 477,652
Gross unrealized gains	4,541	9,295
Gross unrealized losses	(5,699)	(1,908)
Fair value	465,787	485,039
Agency Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	4,616	4,308
Gross unrealized gains	0	0
Gross unrealized losses	(127)	(87)
Fair value	4,489	4,221
Mortgage-Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	311	382
Gross unrealized gains	11	14
Gross unrealized losses	0	0
Fair value	322	396
State And Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	452,031	462,942
Gross unrealized gains	4,529	9,280
Gross unrealized losses	(5,383)	(1,738)
Fair value	451,177	470,484
Corporate Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	9,987	10,020
Gross unrealized gains	1	1
Gross unrealized losses	(189)	(83)
Fair value	$ 9,799	$ 9,938