Summary of Significant Accounting Policies - Schedule of Comparative Transition Period Condensed Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended								9 Months Ended	12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Interest income									$ 62,223	$ 73,210	$ 75,580	$ 84,939
Interest expense									14,117	4,429	4,344	22,013
Net interest income	$ 17,015	$ 17,286	$ 17,424	$ 17,056	$ 17,501	$ 17,558	$ 17,862	$ 18,315	48,106	68,781	71,236	62,926
Provision for loan losses	(5,086)	(22,410)	(646)	(1,354)	(3,281)	(1,304)	0	0	275	(29,496)	(4,585)	950
Net interest income after provision for loan losses									47,831	98,277	75,821	61,976
Non-interest income	7,772	8,721	9,738	8,740	8,962	8,015	7,610	5,932	159,533	34,971	30,519	167,036
Non-interest expense	18,149	22,552	23,263	20,973	24,621	21,915	22,855	22,317	95,732	84,937	91,708	131,400
Income before income taxes	11,724	25,865	4,545	6,177	5,123	4,962	2,617	1,930	111,632	48,311	14,632	97,612
Income tax expense (benefit)	3,103	10,394	(102,976)	32	0	0	10	0	9	(89,447)	10	9
Net income	$ 8,621	$ 15,471	$ 107,521	$ 6,145	$ 5,123	$ 4,962	$ 2,607	$ 1,930	111,623	137,758	14,622	97,603
Preferred stock dividends in arrears									(2,538)	0	0	(4,200)
Preferred stock discount accretion									(6,167)	0	0	(8,010)
Retirement of preferred shares									104,000	0	0	104,000
Net income available to common equity									$ 206,918	$ 137,758	$ 14,622	$ 189,393