Note 21 - Fair Value Measurements - Fair Value of Financial Assets Measure on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Available-for-sale securities	$ 1,317,420	$ 1,157,354
Assets held in trading accounts	49	41
Fair Value, Measurements, Recurring [Member]
Assets held in trading accounts	49	41
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets held in trading accounts
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets held in trading accounts	49	41
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets held in trading accounts
US Government Agencies Debt Securities [Member]
Available-for-sale securities	208,220	137,771
US Government Agencies Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities	208,220	137,771
US Government Agencies Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities
US Government Agencies Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale securities	208,220	137,771
US Government Agencies Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale securities
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Available-for-sale securities	959,698	868,324
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities	959,698	868,324
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale securities	959,698	868,324
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale securities
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	84,822	102,943
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities	84,822	102,943
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale securities	84,822	102,943
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale securities
Other Securities [Member]
Available-for-sale securities	64,680	48,016
Other Securities [Member] | Fair Value, Measurements, Recurring [Member]
Other securities	64,680	48,016
Other Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Other securities
Other Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Other securities	64,680	48,016
Other Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Other securities
US Treasury Securities [Member]
Available-for-sale securities		300
US Treasury Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities		300
US Treasury Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities		300
US Treasury Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale securities
US Treasury Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Available-for-sale securities