Deposits - Composition of Deposits (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Sep. 30, 2015
Composition of deposits:
Noninterest-bearing demand	$ 1,880,512	$ 1,368,453
NOW accounts, money market and savings	5,343,183	4,638,446
Time deposits, $250,000 or more	265,904	217,016
Other time deposits	1,115,191	1,163,150
Total deposits	$ 8,604,790	$ 7,387,065