Securities (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) security	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) security	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) security
Securities
Number of securities held with unrealized loss | security	70		70		80
Proceeds from sales of securities available-for-sale			$ 19,026	$ 14,447
Gain on sales of securities	$ 0	$ 141	72	$ 141
Total available-for-sale securities	447,458		447,458		$ 384,359
Held-to-maturity Securities	2,197,629		2,197,629		2,133,804
Held-to-maturity securities, fair value	2,215,444		2,215,444		2,131,371
Callable securities, amortized cost	306,000		306,000
Callable securities amortized cost, callable within one year and thereafter	289,600		289,600
Accrued interest receivable for securities	7,300		7,300		$ 6,700
Available-for-sale debt securities, excluding mortgage-backed securities
Securities
Available-for-sale debt securities, amortized cost	98,700		98,700
Total available-for-sale securities	98,200		98,200
Held-to-maturity debt securities, excluding mortgage-backed securities
Securities
Held-to-maturity Securities	237,800		237,800
Held-to-maturity securities, fair value	$ 238,100		$ 238,100