Condensed Financial Statements of Parent Company - Summary of Condensed Statements of Cash Flows of Parent Company (Detail) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash Flows from Operating Activities:
Net income	$ 17,786	$ 15,289	$ 11,556	$ 13,952	$ 58,583	$ 43,214	$ 32,694
Adjustments to reconcile net income to net cash used in operating activities:
(Increase) decrease in other assets					(12,024)	(16,423)	(15,091)
Increase (decrease) in other liabilities					8,706	9,606	6,974
Net Cash (Used in) Provided by Operating Activities					(356,648)	(542,498)	722,035
Cash Flows from Investing Activities:
Purchases of investment securities available for sale					(231,703)	(164,940)	(542,110)
Net Cash Used in Investing Activities					(1,258,226)	(1,921,920)	(1,588,015)
Cash Flows from Financing Activities:
Proceeds from issuance of common stock					806	77	97,507
Net proceeds from issuance of preferred stock					55,569	0	0
Proceeds from issuance of long-term debt					0	133,142	60,336
Exercise and redemption of warrants					98	6	264
Preferred stock dividends paid					(2,314)	0	0
Purchase of treasury stock					0	0	(7,754)
Net Cash Provided by Financing Activities					1,508,444	2,602,373	913,032
Net Increase (Decrease) in Cash and Cash Equivalents					(106,430)	137,955	47,052
Cash and Cash Equivalents – Beginning				371,023	371,023	233,068	186,016
Cash and Cash Equivalents – Ending	264,593				264,593	371,023	233,068
The Customer Bancorp
Cash Flows from Operating Activities:
Net income					58,583	43,214	32,694
Adjustments to reconcile net income to net cash used in operating activities:
Equity in undistributed earnings of subsidiaries, net of dividends received from Bank					(46,980)	(50,189)	(35,658)
(Increase) decrease in other assets					2,488	(1,354)	(1,465)
Increase (decrease) in other liabilities					(112)	1,497	(281)
Net Cash (Used in) Provided by Operating Activities					13,979	(6,832)	(4,710)
Cash Flows from Investing Activities:
Purchases of investment securities available for sale					0	0	0
Payments for investments in and advances to subsidiaries					(30,036)	(15,032)	(177,068)
Net Cash Used in Investing Activities					(30,036)	(15,032)	(177,068)
Cash Flows from Financing Activities:
Proceeds from issuance of common stock					904	77	97,507
Net proceeds from issuance of preferred stock					55,569	0	0
Proceeds from issuance of long-term debt					0	25,000	60,336
Exercise and redemption of warrants					0	6	264
Payments on partial shares for stock dividend					0	(8)	0
Preferred stock dividends paid					(2,314)	0	0
Purchase of treasury stock					0	0	(7,754)
Net Cash Provided by Financing Activities					54,159	25,075	150,353
Net Increase (Decrease) in Cash and Cash Equivalents					38,102	3,211	(31,425)
Cash and Cash Equivalents – Beginning				$ 16,465	16,465	13,254	44,679
Cash and Cash Equivalents – Ending	$ 54,567				$ 54,567	$ 16,465	$ 13,254