Investment Securities (Narrative) (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) securities	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) securities	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Transfer of available-for-sale securities to held-to-maturity securities									$ 0	$ 862,712	$ 0
Available-for-sale securities, transferred to held-to-maturity, unrealized gain(loss)										14,400
Income tax expense	$ 33,724	$ 31,939	$ 29,930	$ 29,386	$ 20,896	$ 23,842	$ 26,295	$ 23,983	124,979	95,016	95,033
Investment securities pledged as collateral	$ 1,400,000				$ 1,200,000				$ 1,400,000	1,200,000
Number of securities by a single non-goverment sponsored issuer exceeding 10% of shareholders' equity | securities	0								0
Available-for-sale securities
Schedule of Available-for-sale Securities [Line Items]
Income tax expense									$ 2,900	$ 122	$ 194