Acquisitions - Narrative (Details) $ / shares in Units, $ in Thousands			3 Months Ended
	Jun. 30, 2019 USD ($)	Jul. 01, 2018 USD ($) shares	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jun. 29, 2018 $ / shares
Business Acquisition [Line Items]
Goodwill				$ 808,322	$ 808,726
Grandpoint Capital, Inc.
Business Acquisition [Line Items]
Total assets acquired	$ 3,076,224	$ 3,051,567	$ 3,076,224
Gross loans acquired		2,400,000
Total deposits acquired	2,506,929	$ 2,506,663	2,506,929
Equity issued, ratio		0.4750
Consideration paid	602,152	$ 602,200
Aggregate cash consideration payable		28,100
Company's common stock value (usd per share) | $ / shares						$ 38.15
Goodwill	$ 312,639	$ 312,600	312,639
Net adjustment to loans, deferred tax assets and other assets since acquisition			$ 580
Grandpoint Capital, Inc. | Common Stock
Business Acquisition [Line Items]
Common stock issued as consideration (in shares) | shares		15,758,089