Bank segment - Contractual maturities of securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Amortized cost
Due in one year or less	$ 9,998
Due after one year through five years	77,138
Due after five years through ten years	81,464
Due after ten years	29,362
Total amortized cost	197,962
Mortgage-related securities-FNMA, FHLMC and GNMA	1,131,245
Amortized cost	1,329,207	$ 1,118,350
Fair value
Due in one year or less	9,999
Due after one year through five years	77,331
Due after five years through ten years	81,170
Due after ten years	29,045
Total fair value	197,545
Mortgage-related securities-FNMA, FHLMC and GNMA	1,122,565
Available-for-sale securities	$ 1,320,110	$ 1,105,182