Condensed Financial Statements of Parent Company - Summary of Condensed Income Statements of Parent Company (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating expense:
Interest	$ 12,175	$ 11,084	$ 8,162	$ 7,082	$ 6,803	$ 6,547	$ 5,557	$ 5,394	$ 38,504	$ 24,301	$ 21,761
Income tax benefit	(7,289)	(3,940)	(5,517)	(3,429)	(4,810)	(4,494)	(4,429)	(3,871)	(20,174)	(17,604)	(12,272)
Net income									43,214	32,694	23,818
The Customer Bancorp
Operating income:
Other									90	758	0
Total operating income									90	758	0
Operating expense:
Interest									5,251	1,923	0
Other									5,611	3,395	2,708
Total operating expense									10,862	5,318	2,708
Loss before taxes and undistributed income of subsidiaries									(10,772)	(4,560)	(2,708)
Income tax benefit									3,797	1,596	948
Loss before undistributed income of subsidiaries									(6,975)	(2,964)	(1,760)
Equity in undistributed income of subsidiaries									50,189	35,658	25,578
Net income									$ 43,214	$ 32,694	$ 23,818