Summary of Significant Accounting Policies - CECL Adjustments (Details) - USD ($) $ in Thousands	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses		$ (52,162)	$ (120,185)
Deferred tax assets, net		27,282	37,536
Remaining purchase discount on loans		(50,958)
Reserve for unfunded commitments		946
Retained earnings		$ 617,355	$ 571,709
Cumulative Effect, Period Of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	$ (42,484)
Deferred tax assets, net	12,305
Remaining purchase discount on loans	5,469
Reserve for unfunded commitments	10,389
Retained earnings	(35,099)
Cumulative Effect, Period Of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for credit losses	(94,646)
Deferred tax assets, net	39,587
Remaining purchase discount on loans	(45,489)
Reserve for unfunded commitments	11,335
Retained earnings	$ 582,256