Business Combinations (Statement of Assets Acquired and Liabilities Assumed at Estimated Fair Values) (Details) (USD $) In Thousands, unless otherwise specified	0 Months Ended
	Apr. 18, 2014	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair value of liabilities assumed:
Goodwill		$ 1,788,640	$ 1,786,225	$ 764,305
Sterling Financial Corporation [Member]
Fair value of consideration:
Cash paid	136,200
Liability recorded for warrants' cash payment per share	6,453
Fair value of common shares issued	1,939,497
Fair value of warrants, common stock options, and restricted stock exchanged	50,317
Total consideration	2,132,467
Fair value of assets acquired:
Cash and equivalents	253,067
Investment securities	1,378,300
Loans held for sale	214,911
Non-covered loans and leases, net	7,123,168
Premises and equipment	116,576
Residential mortgage servicing rights	62,770
Other intangible assets	54,562
Other real estate owned	8,666
Bank owned life insurance	193,246
Deferred tax asset	300,015
Accrued interest receivable	23,553
Other assets	148,906
Total assets acquired	9,877,740
Fair value of liabilities assumed:
Deposits	7,086,052
Securities sold under agreements to repurchase	584,746
Term debt	854,737
Junior subordinated debentures	156,171
Other liabilities	87,902
Total liabilities assumed	8,769,608
Net assets acquired	1,108,132
Goodwill	$ 1,024,335