Goodwill and Other Intangible Assets - Goodwill and Other Intangibles (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 845,687	$ 842,651
Total	91,334	106,071
Total goodwill and other intangible assets	937,021	948,722
Core deposit intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	105,984	105,984
Accumulated amortization	(26,177)	(16,659)
Total	79,807	89,325
Books of Business Intangible
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	15,234	15,414
Accumulated amortization	(3,707)	(2,827)
Total	11,527	12,587
Other intangibles
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	2,068	6,037
Accumulated amortization	(2,068)	(1,878)
Total	$ 0	$ 4,159