Fair value measurements (Details 2) - USD ($)	Sep. 30, 2015	Dec. 31, 2014
Fair value measurements on a recurring basis
Available-for-sale securities	$ 785,837,000	$ 550,394,000
Estimated fair value
Fair value measurements on a recurring basis
Money market funds	10,000	10,000
Available-for-sale securities	785,837,000	550,394,000
Derivative assets
Derivative assets	586,000	398,000
Derivative liabilities
Derivative liabilities	125,000	114,000
Loans	4,700,042,000	4,578,822,000
Level 1 | Interest rate lock commitments
Derivative liabilities
Derivative liabilities	0	0
Level 1 | Estimated fair value
Derivative assets
Derivative assets	0	0
Derivative liabilities
Derivative liabilities	112,000	71,000
Level 2 | Estimated fair value
Fair value measurements on a recurring basis
Money market funds	10,000	10,000
Available-for-sale securities	785,837,000	550,394,000
Derivative assets
Derivative assets	586,000	398,000
Derivative liabilities
Derivative liabilities	13,000	43,000
Level 3 | Estimated fair value
Derivative liabilities
Loans	4,700,042,000	4,578,822,000
Fair value measurements on a recurring basis | Level 1
Derivative assets
Derivative assets	0	0
Derivative liabilities
Derivative liabilities	112,000	71,000
Fair value measurements on a recurring basis | Level 1 | Forward sale contracts
Derivative assets
Derivative assets	0	0
Derivative liabilities
Derivative liabilities	112,000	71,000
Fair value measurements on a recurring basis | Level 2
Derivative assets
Derivative assets	586,000	398,000
Derivative liabilities
Derivative liabilities	13,000	43,000
Fair value measurements on a recurring basis | Level 2 | Interest rate lock commitments
Derivative assets
Derivative assets	585,000	393,000
Derivative liabilities
Derivative liabilities	0	3,000
Fair value measurements on a recurring basis | Level 2 | Forward sale contracts
Derivative assets
Derivative assets	1,000	5,000
Derivative liabilities
Derivative liabilities	13,000	40,000
Fair value measurements on a recurring basis | Level 2 | Other
Fair value measurements on a recurring basis
Money market funds	10,000	10,000
Fair value measurements on a recurring basis | Level 2 | Bank
Fair value measurements on a recurring basis
Available-for-sale securities	785,837,000	550,394,000
Fair value measurements on a recurring basis | Level 2 | Mortgage-related securities - FNMA, FHLMC and GNMA | Bank
Fair value measurements on a recurring basis
Available-for-sale securities	574,719,000	430,834,000
Fair value measurements on a recurring basis | Level 2 | U.S. Treasury federal agency obligations | Bank
Fair value measurements on a recurring basis
Available-for-sale securities	211,118,000	119,560,000
Fair value measurements on a nonrecurring basis | American Savings Bank (ASB)
Derivative liabilities
Adjustments to fair value of loans held for sale	0	0
Fair value measurements on a nonrecurring basis | Estimated fair value
Derivative liabilities
Loans	951,000	2,445,000
Real estate acquired in settlement of loans	70,000	288,000
Fair value measurements on a nonrecurring basis | Level 3
Derivative liabilities
Loans	951,000	2,445,000
Real estate acquired in settlement of loans	$ 70,000	$ 288,000