Note 14 - Regulatory Capital - Summary of the Bank's Compliance (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Savings Bank [Member]
Tier I (leverage) capital:
Tier i (leverage) capital, capital level, amount	$ 607,033	$ 494,690
Tier i (leverage) capital, capital level, percent	10.12%	8.89%
Tier i (leverage) capital, requirement to be well capitalized, amount	$ 299,848	$ 278,175
Tier i (leverage) capital, requirement to be well capitalized, percent	5.00%	5.00%
Tier i (leverage) capital, excess, amount	$ 307,185	$ 216,515
Tier i (leverage) capital, excess, percent	5.12%	3.89%
Common Equity Tier I risk-based capital:
Common equity tier i risk-based capital, capital level, amount	$ 607,033	$ 494,690
Common equity tier i risk-based capital, capital level, percent	14.12%	12.62%
Common equity tier i risk-based capital, requirement to be well capitalized, amount	$ 279,443	$ 254,768
Common equity tier i risk-based capital, requirement to be well capitalized, percent	6.50%	6.50%
Common equity tier i risk-based capital, excess, amount	$ 327,590	$ 239,922
Common equity tier i risk-based capital, excess, percent	7.62%	6.12%
Tier I risk-based capital:
Tier 1 risk-based capital, capital level, amount	$ 607,033	$ 494,690
Tier 1 risk-based capital, capital level, percent	14.12%	12.62%
Tier 1 risk-based capital, requirement to be well capitalized, amount	$ 343,930	$ 313,560
Tier 1 risk-based capital, requirement to be well capitalized, percent	8.00%	8.00%
Tier 1 risk-based capital, excess, amount	$ 263,103	$ 181,130
Tier 1 risk-based capital, excess, percent	6.12%	4.62%
Total risk-based capital:
Total risk-based capital, capital level, amount	$ 629,262	$ 516,226
Total risk-based capital, capital level, percent	14.64%	13.17%
Total risk-based capital, requirement to be well capitalized, amount	$ 429,913	$ 391,950
Total risk-based capital, requirement to be well capitalized, percent	10.00%	10.00%
Total risk-based capital, excess, amount	$ 199,349	$ 124,276
Total risk-based capital, excess, percent	4.64%	3.17%
Holding Company [Member]
Tier I (leverage) capital:
Tier i (leverage) capital, capital level, amount	$ 539,228	$ 490,919
Tier i (leverage) capital, capital level, percent	9.00%	8.84%
Tier i (leverage) capital, requirement to be well capitalized, amount	$ 299,654	$ 277,611
Tier i (leverage) capital, requirement to be well capitalized, percent	5.00%	5.00%
Tier i (leverage) capital, excess, amount	$ 239,574	$ 213,308
Tier i (leverage) capital, excess, percent	4.00%	3.84%
Common Equity Tier I risk-based capital:
Common equity tier i risk-based capital, capital level, amount	$ 506,432	$ 462,883
Common equity tier i risk-based capital, capital level, percent	11.79%	11.83%
Common equity tier i risk-based capital, requirement to be well capitalized, amount	$ 279,121	$ 254,335
Common equity tier i risk-based capital, requirement to be well capitalized, percent	6.50%	6.50%
Common equity tier i risk-based capital, excess, amount	$ 227,311	$ 208,548
Common equity tier i risk-based capital, excess, percent	5.29%	5.33%
Tier I risk-based capital:
Tier 1 risk-based capital, capital level, amount	$ 539,228	$ 490,919
Tier 1 risk-based capital, capital level, percent	12.56%	12.55%
Tier 1 risk-based capital, requirement to be well capitalized, amount	$ 343,534	$ 313,028
Tier 1 risk-based capital, requirement to be well capitalized, percent	8.00%	8.00%
Tier 1 risk-based capital, excess, amount	$ 195,694	$ 177,891
Tier 1 risk-based capital, excess, percent	4.56%	4.55%
Total risk-based capital:
Total risk-based capital, capital level, amount	$ 636,457	$ 512,454
Total risk-based capital, capital level, percent	14.82%	13.10%
Total risk-based capital, requirement to be well capitalized, amount	$ 429,417	$ 391,285
Total risk-based capital, requirement to be well capitalized, percent	10.00%	10.00%
Total risk-based capital, excess, amount	$ 207,040	$ 121,169
Total risk-based capital, excess, percent	4.82%	3.10%