Fair Value Measurements - Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financial assets:
Trading securities	$ 373,300	$ 265,534
Available for sale securities	755,546	598,007
Financial liabilities:
Securities sold, not yet purchased, at fair value	144,193	153,889
Recurring
Financial assets:
Trading securities	373,300	265,534
Available for sale securities	755,546	598,007
Loans held for sale	1,274,232	1,748,498
Derivative assets	72,906	57,036
Mortgage servicing asset	45,573	61,968
Financial liabilities:
Securities sold, not yet purchased, at fair value	144,193	153,889
Derivative liabilities	37,024	35,737
Recurring | Level 1
Financial assets:
Trading securities	3,640	9,481
Available for sale securities	20,263	19,840
Financial liabilities:
Securities sold, not yet purchased, at fair value	75,047	60,715
Recurring | Level 2
Financial assets:
Trading securities	369,660	256,053
Available for sale securities	735,283	578,167
Loans held for sale	1,244,018	1,712,697
Derivative assets	72,906	57,036
Financial liabilities:
Securities sold, not yet purchased, at fair value	69,146	93,174
Derivative liabilities	37,024	35,737
Recurring | Level 3
Financial assets:
Loans held for sale	30,214	35,801
Mortgage servicing asset	$ 45,573	$ 61,968