Fair Value Measurements - Assets measured on a recurring basis (Details) - Fair Value, measurements, recurring - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Other Trading Assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year		$ 0	$ 859
Total gains or losses (realized/unrealized):
Included in earnings	[1]	0	(40)
Purchases, issuances, sales and settlements:
Balance, end of year		0	819
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held		0	(40)
Interest rate contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year		2,416	2,392
Total gains or losses (realized/unrealized):
Included in earnings	[1]	192	785
Purchases, issuances, sales and settlements:
Balance, end of year		2,608	3,177
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held		192	785
Other assets - MSRs
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year		49,597	51,428
Total gains or losses (realized/unrealized):
Included in earnings	[1]	1,885	(2,670)
Purchases, issuances, sales and settlements:
Issuances		1,543	2,018
Balance, end of year		53,025	50,776
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held		1,885	(2,670)
Other assets - SBIC investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year		45,042	15,639
Total gains or losses (realized/unrealized):
Included in earnings	[1]		550
Purchases, issuances, sales and settlements:
Purchases		2,945	6,364
Balance, end of year		47,987	22,553
Change in unrealized gains (losses) included in earnings for the period, attributable to assets and liabilities still held		$ 0	$ 550

[1] Included in noninterest income in the Unaudited Condensed Consolidated Statements of Income.