Bank segment - Contractual maturities of securities (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) security	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Amortized cost
Due in one year or less		$ 9,992
Due after one year through five years		77,151
Due after five years through ten years		85,724
Due after ten years		29,849
Total amortized cost		202,716
Mortgage-related securities-FNMA, FHLMC and GNMA - amortized cost		1,109,613
Amortized cost		1,312,329		$ 1,118,350
Fair value
Due in one year or less		9,993
Due after one year through five years		77,307
Due after five years through ten years		85,258
Due after ten years		29,452
Total fair value		202,010
Mortgage-related securities-FNMA, FHLMC and GNMA - fair value		1,100,876
Available-for-sale securities		$ 1,302,886		$ 1,105,182
Gross realized gains from the sale of available-for-sale investment securities	$ 16,400		$ 600
Gross realized losses from the sale of available-for-sale investment securities	$ 0		$ 0
Number of available-for-sale investment securities sold during period | security		0