Fair Value Measurements - Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financial assets:
Trading securities	$ 660,314	$ 730,685
Available for sale securities	874,496	744,319
Equity securities	21,555	21,241
Financial liabilities:
Securities sold, not yet purchased	179,582	232,821
Recurring
Financial assets:
Trading securities	660,314	730,685
Available for sale securities	874,496	744,319
Equity securities	21,555	21,241
Loans held for sale	1,387,622	1,581,603
Derivative assets	45,979	34,150
MSR asset	68,804	54,714
Financial liabilities:
Securities sold, not yet purchased	179,582	232,821
Derivative liabilities	15,291	13,197
Recurring | Level 1
Financial assets:
Trading securities	2,341	3,329
Equity securities	21,555	21,241
Financial liabilities:
Securities sold, not yet purchased	116,965	156,586
Recurring | Level 2
Financial assets:
Trading securities	657,973	727,356
Available for sale securities	874,496	744,319
Loans held for sale	1,333,257	1,544,631
Derivative assets	45,979	34,150
Financial liabilities:
Securities sold, not yet purchased	62,617	76,235
Derivative liabilities	15,291	13,197
Recurring | Level 3
Financial assets:
Loans held for sale	54,365	36,972
MSR asset	$ 68,804	$ 54,714