Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income		$ 55,424	$ 42,821	$ 112,210	$ 87,002
Unrealized gains and losses on debt securities:
Change in unrealized holding gains and losses, net		(16,020)	35,311	(96,682)	57,582
Less: Reclassification adjustment for gains included in net income		(228)	(1,280)	(367)	(1,748)
Change in unrealized gains and losses on debt securities during the period		(16,248)	34,031	(97,049)	55,834
Change in unrealized gains and losses on derivative hedges		910	(1,157)	3,112	(911)
Income tax benefit (expense)		3,770	(12,340)	23,552	(21,006)
Other comprehensive (loss) income before reclassifications		(11,568)	20,534	(70,385)	33,917
Amounts reclassified from accumulated other comprehensive income	[1],[2]			(13,049)
Net current-period other comprehensive (loss) income		(11,568)	20,534	(83,434)	33,917
Comprehensive income		$ 43,856	$ 63,355	$ 28,776	$ 120,919

[1] See Note 3, “New Accounting Pronouncements,” for discussion of the Company’s adoption of ASU No. 2018-02.

[2] See Note 3, “New Accounting Pronouncements,” for discussion of the Company’s adoption of Accounting Standards Update (ASU) No. 2016-01.