Parent Only Statements - Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income	$ 19,717	$ 82,926	$ 44,128	$ 47,014	$ 274,284	$ 193,785	$ 257,593
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Interest income on tax indemnification receivable					(5,398)	(5,904)	0
Decrease in tax indemnification receivable					59,633	44,724	0
Increase in other assets					(18,070)	(24,959)	(2,357)
Increase (decrease) in income tax payable, net					56,813	(221,222)	56,784
(Decrease) increase in payable due to entity that is a subsidiary of Navient					(6,774)	8,764	147,379
Increase in other liabilities					(14,731)	(2,652)	39,096
Total adjustments					(365,487)	(630,558)	(187,573)
Total net cash (used in) provided by operating activities					(91,203)	(436,773)	70,020
Cash flows from investing activities:
Net cash provided by (used in) investing activities					(1,847,509)	(1,388,371)	(731,116)
Cash flows from financing activities:
Special cash contribution from Navient					0	472,718	0
Excess tax benefit from the exercise of stock-based awards					6,140	3,271	6,258
Preferred stock dividends paid					(19,595)	(12,933)	0
Net cash (used in) provided by financing activities					1,995,151	2,002,059	1,244,879
Net (decrease) increase in cash and cash equivalents					56,439	176,915	583,783
Cash and cash equivalents	2,359,780				2,416,219	2,359,780	2,182,865	$ 1,599,082
Cash and cash equivalents at end of year	2,359,780				2,416,219	2,359,780	2,182,865
Parent Company
Cash flows from operating activities:
Net income					274,284	193,785	257,593
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Undistributed earnings of subsidiaries					(295,638)	(211,479)	(394,270)
Interest income on tax indemnification receivable					(5,398)	(5,904)	0
(Increase) decrease in investment in subsidiaries, net					(103,602)	278,365	136,677
Decrease in tax indemnification receivable					59,633	44,724	0
Decrease (increase) in due from subsidiaries, net					11,012	(32,408)	0
Increase in other assets					(14,366)	(5,447)	0
Increase (decrease) in income tax payable, net					(54,907)	(312,770)	0
(Decrease) increase in payable due to entity that is a subsidiary of Navient					(6,774)	8,764	0
Increase in other liabilities					1,402	14,398	0
Total adjustments					(408,638)	(221,757)	(257,593)
Total net cash (used in) provided by operating activities					(134,354)	(27,972)	0
Cash flows from investing activities:
Net cash provided by (used in) investing activities					0	0	0
Cash flows from financing activities:
Special cash contribution from Navient					0	472,718	0
Excess tax benefit from the exercise of stock-based awards					1,740	2,432	0
Preferred stock dividends paid					(19,595)	(12,933)	0
Net cash (used in) provided by financing activities					(17,855)	462,217	0
Net (decrease) increase in cash and cash equivalents					(152,209)	434,245	0
Cash and cash equivalents	434,245				282,036	434,245	0	$ 0
Cash and cash equivalents at end of year	$ 434,245				$ 282,036	$ 434,245	$ 0