Securities - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) security	Dec. 31, 2014 USD ($) security	Dec. 31, 2013 USD ($)
Investments, Debt and Equity Securities [Abstract]
Number of securities held with unrealized loss | security	129	80
Proceeds from sales of securities available-for-sale	$ 19,026	$ 14,447	$ 41,640
Gross realized gains from sale of available for sale securities	72	141	$ 2,057
Securities
Carrying value of available-for-sale securities	416,798	384,359
Held-to-maturity, amortized cost	2,296,799	2,133,804
Held-to-maturity securities, fair value	2,286,092	2,131,371
Callable securities, amortized cost	252,700
Callable securities amortized cost, callable within one year and thereafter	236,300
Accrued interest receivable for securities	7,400	$ 6,700
Available-for-sale debt securities, excluding mortgage-backed securities
Securities
Available-for-sale debt securities, amortized cost	73,700
Carrying value of available-for-sale securities	71,900
Held-to-maturity debt securities, excluding mortgage-backed securities
Securities
Held-to-maturity, amortized cost	239,400
Held-to-maturity securities, fair value	$ 237,600