Acquisition - Pro Forma Financial Information (Details) - MBT - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Total revenue (net interest income plus other income)	$ 120,606	$ 351,121	$ 474,842
Net income	$ 30,835	$ 110,958	$ 174,900
Basic (in dollars per share)	$ 0.55	$ 1.98	$ 3.13
Diluted (in dollars per share)	$ 0.54	$ 1.97	$ 3.12