Subordinated Debentures - Schedule of Convertible Note (Details)			6 Months Ended	12 Months Ended
	Jun. 07, 2018 USD ($) $ / shares	Apr. 26, 2018 USD ($) $ / shares	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($)	Jun. 30, 2018 USD ($)	May 11, 2018 USD ($)
Debt Instrument [Line Items]
Proceeds from convertible notes, net of issuance fees				$ 0	$ 212,920,000	$ 0
Repurchase of treasury stock				$ 13,820,000	$ 150,000,000
Common stock repurchased and recorded as treasury stock (in shares) | shares				943,094	9,002,453
Convertible Notes
Debt Instrument [Line Items]
Aggregate principal amount issued			$ 217,500,000		$ 217,500,000		$ 217,500,000	$ 200,000,000
Initial Rate								2.00%
Additional face amount issued as part of initial offering over-allotment option	$ 17,500,000
Initial conversion rate	0.0450760			0.0450760
Initial conversion price (in dollars per share) | $ / shares	$ 22.18
Premium percentage to closing stock price on date of pricing of the notes	22.50%
Call option, percentage of principal amount in cash	100.00%
Amount of proceeds from convertible notes authorized for repurchase of common stock	100.00%
Proceeds from convertible notes, net of issuance fees		$ 100,000,000.0
Proceeds from convertible notes, net of issuance fees		213,200,000
Proceeds down-streamed to the Bank as equity		113,200,000
Repurchase of treasury stock		$ 76,000,000.0	24,000,000.0
Closing price of common stock (in dollars per share) | $ / shares		$ 18.11
Amortization/ Capitalization Period	5 years			5 years	5 years
Gross Carrying Amount
Convertible notes principal balance			217,500,000	$ 217,500,000	$ 217,500,000
Discount			(21,880,000)	(21,880,000)	(21,880,000)
Issuance costs to be capitalized			(4,119,000)	(4,119,000)	(4,119,000)
Carrying balance of convertible notes			191,501,000	191,501,000	191,501,000
Accumulated Amortization / Capitalization
Discount			2,544,000	6,659,000	2,544,000
Issuance costs to be capitalized			498,000	1,298,000	498,000
Carrying balance of convertible notes			3,042,000	7,957,000	3,042,000
Carrying Amount
Discount			(19,336,000)	(15,221,000)	(19,336,000)
Issuance costs to be capitalized			(3,621,000)	(2,821,000)	(3,621,000)
Carrying balance of convertible notes			$ 194,543,000	199,458,000	194,543,000
Interest expense on convertible notes				$ 9,300,000	$ 5,800,000
Discount Rate | Convertible Notes
Debt Instrument [Line Items]
Discount rate	0.0425