Securities (Securities in a Continuous Unrealized Loss Position) (Details) $ in Thousands	Sep. 30, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Number of securities in a continuous unrealized loss position for less than 12 months | security	49	31
Fair value of securities in a continuous unrealized loss position for less than 12 months	$ 315,564	$ 199,567
Unrealized losses of securities in a continuous unrealized loss position for less than 12 months	$ (8,620)	$ (1,416)
Number of securities in a continuous unrealized loss position for 12 months or longer | security	55	40
Fair value of securities in a continuous unrealized loss position for 12 months or longer	$ 434,212	$ 395,580
Unrealized losses of securities in a continuous unrealized loss position for 12 months or longer	$ (26,192)	$ (12,119)
Number of securities in a continuous unrealized loss position total | security	104	71
Fair value of securities in a continuous unrealized loss position total	$ 749,776	$ 595,147
Unrealized losses of securities in a continuous unrealized loss position total	$ (34,812)	$ (13,535)
Obligations of U.S. government-sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities in a continuous unrealized loss position for less than 12 months | security	8	8
Fair value of securities in a continuous unrealized loss position for less than 12 months	$ 77,958	$ 69,681
Unrealized losses of securities in a continuous unrealized loss position for less than 12 months	$ (2,040)	$ (798)
Number of securities in a continuous unrealized loss position for 12 months or longer | security	11	8
Fair value of securities in a continuous unrealized loss position for 12 months or longer	$ 105,606	$ 87,923
Unrealized losses of securities in a continuous unrealized loss position for 12 months or longer	$ (5,894)	$ (3,077)
Number of securities in a continuous unrealized loss position total | security	19	16
Fair value of securities in a continuous unrealized loss position total	$ 183,564	$ 157,604
Unrealized losses of securities in a continuous unrealized loss position total	$ (7,934)	$ (3,875)
Mortgage-backed securities issued by U.S. government-sponsored agencies and U.S. government-sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities in a continuous unrealized loss position for less than 12 months | security	37	20
Fair value of securities in a continuous unrealized loss position for less than 12 months	$ 235,900	$ 128,965
Unrealized losses of securities in a continuous unrealized loss position for less than 12 months	$ (6,567)	$ (613)
Number of securities in a continuous unrealized loss position for 12 months or longer | security	34	22
Fair value of securities in a continuous unrealized loss position for 12 months or longer	$ 304,937	$ 279,693
Unrealized losses of securities in a continuous unrealized loss position for 12 months or longer	$ (18,472)	$ (7,120)
Number of securities in a continuous unrealized loss position total | security	71	42
Fair value of securities in a continuous unrealized loss position total	$ 540,837	$ 408,658
Unrealized losses of securities in a continuous unrealized loss position total	$ (25,039)	$ (7,733)
Individual name issuer trust preferred debt securities
Schedule of Available-for-sale Securities [Line Items]
Number of securities in a continuous unrealized loss position for less than 12 months | security	0	0
Fair value of securities in a continuous unrealized loss position for less than 12 months	$ 0	$ 0
Unrealized losses of securities in a continuous unrealized loss position for less than 12 months	$ 0	$ 0
Number of securities in a continuous unrealized loss position for 12 months or longer | security	5	7
Fair value of securities in a continuous unrealized loss position for 12 months or longer	$ 12,464	$ 16,984
Unrealized losses of securities in a continuous unrealized loss position for 12 months or longer	$ (839)	$ (1,122)
Number of securities in a continuous unrealized loss position total | security	5	7
Fair value of securities in a continuous unrealized loss position total	$ 12,464	$ 16,984
Unrealized losses of securities in a continuous unrealized loss position total	$ (839)	$ (1,122)
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities in a continuous unrealized loss position for less than 12 months | security	4	3
Fair value of securities in a continuous unrealized loss position for less than 12 months	$ 1,706	$ 921
Unrealized losses of securities in a continuous unrealized loss position for less than 12 months	$ (13)	$ (5)
Number of securities in a continuous unrealized loss position for 12 months or longer | security	5	3
Fair value of securities in a continuous unrealized loss position for 12 months or longer	$ 11,205	$ 10,980
Unrealized losses of securities in a continuous unrealized loss position for 12 months or longer	$ (987)	$ (800)
Number of securities in a continuous unrealized loss position total | security	9	6
Fair value of securities in a continuous unrealized loss position total	$ 12,911	$ 11,901
Unrealized losses of securities in a continuous unrealized loss position total	$ (1,000)	$ (805)