Loans Receivable and Allowance for Loan Losses (Composition of Loans Receivable) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Loans receivable and allowance for loan losses
30-59 Days	$ 79,811		$ 82,526
60-89 Days	21,228		25,313
90 Days or More	66,155		62,834
Total Past Due	167,194		170,673
Current	11,302,414		11,739,049
Total	11,469,608		11,909,722
Net unamortized premiums and deferred loan origination costs	44,448		47,726
Loans receivable	11,514,056		11,957,448
Allowance for loan losses	(107,500)	$ (110,500)	(111,600)	$ (118,600)	$ (134,000)	$ (139,000)
Loans receivable, net	11,406,556		11,845,848
Accruing loans:
Loans receivable and allowance for loan losses
30-59 Days	74,950		77,097
60-89 Days	18,260		22,852
90 Days or More	2,971		4,093
Total Past Due	96,181		104,042
Current	11,253,563		11,681,961
Total	11,349,744		11,786,003
Non-accrual loans:
Loans receivable and allowance for loan losses
30-59 Days	4,861		5,429
60-89 Days	2,968		2,461
90 Days or More	63,184		58,741
Total Past Due	71,013		66,631
Current	48,851		57,088
Total	119,864		123,719
Consumer and Other Loans
Loans receivable and allowance for loan losses
30-59 Days	1,067		2,430
60-89 Days	499		962
90 Days or More	6,243		6,040
Total Past Due	7,809		9,432
Current	235,672		239,936
Total	243,481		249,368
Allowance for loan losses	(8,770)	(9,819)	(8,825)	(9,540)	(10,007)	(8,824)
Consumer and Other Loans | Accruing loans:
Loans receivable and allowance for loan losses
30-59 Days	1,067		2,430
60-89 Days	499		962
Total Past Due	1,566		3,392
Current	235,529		239,936
Total	237,095		243,328
Consumer and Other Loans | Non-accrual loans:
Loans receivable and allowance for loan losses
90 Days or More	6,243		6,040
Total Past Due	6,243		6,040
Current	143		0
Total	6,386		6,040
Consumer and Other Loans | Home equity and other consumer
Loans receivable and allowance for loan losses
30-59 Days	1,067		2,430
60-89 Days	499		962
90 Days or More	6,243		6,040
Total Past Due	7,809		9,432
Current	164,318		175,121
Total	172,127		184,553
Consumer and Other Loans | Home equity and other consumer | Accruing loans:
Loans receivable and allowance for loan losses
30-59 Days	1,067		2,430
60-89 Days	499		962
Total Past Due	1,566		3,392
Current	164,175		175,121
Total	165,741		178,513
Consumer and Other Loans | Home equity and other consumer | Non-accrual loans:
Loans receivable and allowance for loan losses
90 Days or More	6,243		6,040
Total Past Due	6,243		6,040
Current	143		0
Total	6,386		6,040
Consumer and Other Loans | Commercial and industrial
Loans receivable and allowance for loan losses
30-59 Days			0
60-89 Days			0
90 Days or More			0
Total Past Due			0
Current	71,354		64,815
Total	71,354		64,815
Consumer and Other Loans | Commercial and industrial | Accruing loans:
Loans receivable and allowance for loan losses
30-59 Days			0
60-89 Days			0
Total Past Due			0
Current	71,354		64,815
Total	71,354		64,815
Consumer and Other Loans | Commercial and industrial | Non-accrual loans:
Loans receivable and allowance for loan losses
90 Days or More			0
Total Past Due			0
Total			0
Mortgage loans (gross)
Loans receivable and allowance for loan losses
30-59 Days	78,744		80,096
60-89 Days	20,729		24,351
90 Days or More	59,912		56,794
Total Past Due	159,385		161,241
Current	11,066,742		11,499,113
Total	11,226,127		11,660,354
Mortgage loans (gross) | Accruing loans:
Loans receivable and allowance for loan losses
30-59 Days	73,883		74,667
60-89 Days	17,761		21,890
90 Days or More	2,971		4,093
Total Past Due	94,615		100,650
Current	11,018,034		11,442,025
Total	11,112,649		11,542,675
Mortgage loans (gross) | Non-accrual loans:
Loans receivable and allowance for loan losses
30-59 Days	4,861		5,429
60-89 Days	2,968		2,461
90 Days or More	56,941		52,701
Total Past Due	64,770		60,591
Current	48,708		57,088
Total	113,478		117,679
Mortgage loans (gross) | Residential
Loans receivable and allowance for loan losses
30-59 Days	70,917		73,326
60-89 Days	19,263		21,290
90 Days or More	52,268		44,989
Total Past Due	142,448		139,605
Current	6,277,786		6,733,931
Total	6,420,234		6,873,536
Allowance for loan losses	(44,546)	(43,481)	(46,283)	(56,552)	(74,717)	(80,337)
Mortgage loans (gross) | Residential | Accruing loans:
Loans receivable and allowance for loan losses
30-59 Days	67,168		69,335
60-89 Days	16,634		19,175
90 Days or More			144
Total Past Due	83,802		88,654
Current	6,232,218		6,684,871
Total	6,316,020		6,773,525
Mortgage loans (gross) | Residential | Non-accrual loans:
Loans receivable and allowance for loan losses
30-59 Days	3,749		3,991
60-89 Days	2,629		2,115
90 Days or More	52,268		44,845
Total Past Due	58,646		50,951
Current	45,568		49,060
Total	104,214		100,011
Mortgage loans (gross) | Residential | Full documentation interest-only
Loans receivable and allowance for loan losses
30-59 Days	11,965		16,314
60-89 Days	3,769		7,690
90 Days or More	12,338		11,502
Total Past Due	28,072		35,506
Current	635,865		818,676
Total	663,937		854,182
Mortgage loans (gross) | Residential | Full documentation interest-only | Accruing loans:
Loans receivable and allowance for loan losses
30-59 Days	10,810		13,943
60-89 Days	3,769		7,332
Total Past Due	14,579		21,275
Current	624,504		804,880
Total	639,083		826,155
Mortgage loans (gross) | Residential | Full documentation interest-only | Non-accrual loans:
Loans receivable and allowance for loan losses
30-59 Days	1,155		2,371
60-89 Days			358
90 Days or More	12,338		11,502
Total Past Due	13,493		14,231
Current	11,361		13,796
Total	24,854		28,027
Mortgage loans (gross) | Residential | Full documentation amortizing
Loans receivable and allowance for loan losses
30-59 Days	32,758		26,082
60-89 Days	6,919		7,849
90 Days or More	21,020		14,355
Total Past Due	60,697		48,286
Current	4,739,329		4,955,407
Total	4,800,026		5,003,693
Mortgage loans (gross) | Residential | Full documentation amortizing | Accruing loans:
Loans receivable and allowance for loan losses
30-59 Days	31,191		25,878
60-89 Days	5,124		7,611
90 Days or More			144
Total Past Due	36,315		33,633
Current	4,731,728		4,948,391
Total	4,768,043		4,982,024
Mortgage loans (gross) | Residential | Full documentation amortizing | Non-accrual loans:
Loans receivable and allowance for loan losses
30-59 Days	1,567		204
60-89 Days	1,795		238
90 Days or More	21,020		14,211
Total Past Due	24,382		14,653
Current	7,601		7,016
Total	31,983		21,669
Mortgage loans (gross) | Residential | Reduced documentation interest-only
Loans receivable and allowance for loan losses
30-59 Days	16,220		19,310
60-89 Days	5,409		3,037
90 Days or More	13,513		16,289
Total Past Due	35,142		38,636
Current	474,902		572,372
Total	510,044		611,008
Mortgage loans (gross) | Residential | Reduced documentation interest-only | Accruing loans:
Loans receivable and allowance for loan losses
30-59 Days	15,684		18,490
60-89 Days	4,917		2,584
Total Past Due	20,601		21,074
Current	451,641		547,350
Total	472,242		568,424
Mortgage loans (gross) | Residential | Reduced documentation interest-only | Non-accrual loans:
Loans receivable and allowance for loan losses
30-59 Days	536		820
60-89 Days	492		453
90 Days or More	13,513		16,289
Total Past Due	14,541		17,562
Current	23,261		25,022
Total	37,802		42,584
Mortgage loans (gross) | Residential | Reduced documentation amortizing
Loans receivable and allowance for loan losses
30-59 Days	9,974		11,620
60-89 Days	3,166		2,714
90 Days or More	5,397		2,843
Total Past Due	18,537		17,177
Current	427,690		387,476
Total	446,227		404,653
Mortgage loans (gross) | Residential | Reduced documentation amortizing | Accruing loans:
Loans receivable and allowance for loan losses
30-59 Days	9,483		11,024
60-89 Days	2,824		1,648
Total Past Due	12,307		12,672
Current	424,345		384,250
Total	436,652		396,922
Mortgage loans (gross) | Residential | Reduced documentation amortizing | Non-accrual loans:
Loans receivable and allowance for loan losses
30-59 Days	491		596
60-89 Days	342		1,066
90 Days or More	5,397		2,843
Total Past Due	6,230		4,505
Current	3,345		3,226
Total	9,575		7,731
Mortgage loans (gross) | Multi-family
Loans receivable and allowance for loan losses
30-59 Days	5,319		4,294
60-89 Days	1,466		2,568
90 Days or More	4,850		8,917
Total Past Due	11,635		15,779
Current	3,932,821		3,897,274
Total	3,944,456		3,913,053
Allowance for loan losses	(38,794)	(40,082)	(39,250)	(37,075)	(34,578)	(36,703)
Mortgage loans (gross) | Multi-family | Accruing loans:
Loans receivable and allowance for loan losses
30-59 Days	5,023		3,646
60-89 Days	1,127		2,222
90 Days or More	737		1,790
Total Past Due	6,887		7,658
Current	3,931,487		3,893,539
Total	3,938,374		3,901,197
Mortgage loans (gross) | Multi-family | Non-accrual loans:
Loans receivable and allowance for loan losses
30-59 Days	296		648
60-89 Days	339		346
90 Days or More	4,113		7,127
Total Past Due	4,748		8,121
Current	1,334		3,735
Total	6,082		11,856
Mortgage loans (gross) | Commercial real estate
Loans receivable and allowance for loan losses
30-59 Days	2,508		2,476
60-89 Days			493
90 Days or More	2,794		2,888
Total Past Due	5,302		5,857
Current	856,135		867,908
Total	861,437		873,765
Allowance for loan losses	(15,390)	$ (17,118)	(17,242)	$ (15,433)	$ (14,698)	$ (13,136)
Mortgage loans (gross) | Commercial real estate | Accruing loans:
Loans receivable and allowance for loan losses
30-59 Days	1,692		1,686
60-89 Days			493
90 Days or More	2,234		2,159
Total Past Due	3,926		4,338
Current	854,329		863,615
Total	858,255		867,953
Mortgage loans (gross) | Commercial real estate | Non-accrual loans:
Loans receivable and allowance for loan losses
30-59 Days	816		790
90 Days or More	560		729
Total Past Due	1,376		1,519
Current	1,806		4,293
Total	$ 3,182		$ 5,812