The component of interest expense representing the noncash expenses charged against earnings in the period to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate caption: Noncash Interest Expense.

No definition available.

Schedule II - Condensed Financial Information of Registrant (Condensed Statements of Cash Flows) (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Aug. 31, 2015	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities
Net income		$ 33,776	$ 97,306	$ 82,845	$ 5,903	$ 31,217	$ 67,815	$ 36,744	$ (9,753)	$ 219,830	$ 126,023	$ 253,283
Adjustments to reconcile net income to net cash provided by operating activities:
Change in fair value of 2015 notes embedded conversion derivative										(464,698)	32,321	133,968
Change in fair value of derivatives										334,300	(506,328)	(1,076,015)
Loss on extinguishment of debt						1,951	$ 0	$ 6,574	3,977	0	12,502	32,515
Share-based compensation										7,373	3,544	10,476
ESOP compensation										2,604	2,486	3,464
Deferred income taxes (benefits)										41,916	(46,504)	3,013
Other										(15,962)	(8,948)	(7,059)
Changes in operating assets and liabilities:
Other assets										71	(2,771)	1,113
Other liabilities										75,794	(51,008)	(11,435)
Net cash provided by operating activities										504,804	707,786	862,668
Investing activities
Net cash used in investing activities										(5,577,205)	(2,947,749)	(3,879,296)
Financing activities
Financing fees incurred and deferred										0	(100)	(11,942)
Repayment of notes payable										(48,152)	(219,094)	(234,154)
Net proceeds from settlement of notes hedges and warrants										25,775	16,558	22,170
Excess tax benefits realized from share-based compensation plans										3,649	5,184	4,043
Proceeds from issuance of common stock	$ 104,500									112,481	13,681	31,764
Dividends paid										(17,874)	(15,015)	(12,643)
Net cash provided by (used in) financing activities										4,768,636	2,043,948	2,645,612
Increase (decrease) in cash and cash equivalents										(303,765)	(196,015)	(371,016)
Cash and cash equivalents at beginning of year					701,514				897,529	701,514	897,529	1,268,545
Cash and cash equivalents at end of year		397,749				701,514				397,749	701,514	897,529
Cash paid during the year for interest:
Interest paid										39,118	42,989	25,608
Parent Company [Member]
Operating activities
Net income										219,830	126,023	253,283
Adjustments to reconcile net income to net cash provided by operating activities:
Change in fair value of 2015 notes embedded conversion derivative										(4,516)	(15,227)	141,974
Provision for depreciation and amortization										1,613	2,081	2,831
Accrual of discount on equity security										(6)	(6)	(5)
Equity in undistributed income of subsidiaries										(209,698)	(134,890)	(279,961)
Accrual of discount on contingent convertible notes										698	4,417	12,417
Change in fair value of derivatives										6,377	15,619	(144,012)
Loss on extinguishment of debt										0	12,502	32,515
Accrual of discount on debenture issued to subsidiary trust										207	193	181
Share-based compensation										1,026	1,141	1,407
ESOP compensation										0	82	110
Deferred income taxes (benefits)										8,967	6,439	(5,202)
Other										0	(2,235)	(3,608)
Changes in operating assets and liabilities:
Receivable from subsidiaries										93	2,208	995
Federal income tax recoverable										2,683	1,121	62
Other assets										(4)	378	(1,945)
Other liabilities										(1,664)	(7,256)	20,131
Net cash provided by operating activities										25,606	12,590	31,173
Investing activities
Capital contributions to subsidiaries										(120,000)	0	0
Net cash used in investing activities										(120,000)	0	0
Financing activities
Financing fees incurred and deferred										0	(100)	(11,942)
Proceeds from notes payable										0	0	415,000
Repayment of notes payable										(48,152)	(219,094)	(234,154)
Net proceeds from settlement of notes hedges and warrants										25,775	16,558	22,170
Excess tax benefits realized from share-based compensation plans										0	184	159
Proceeds from issuance of common stock										112,481	13,681	31,764
Dividends paid										(17,946)	(15,221)	(12,849)
Net cash provided by (used in) financing activities										72,158	(203,992)	210,148
Increase (decrease) in cash and cash equivalents										(22,236)	(191,402)	241,321
Cash and cash equivalents at beginning of year					$ 61,139				$ 252,541	61,139	252,541	11,220
Cash and cash equivalents at end of year		$ 38,903				$ 61,139				38,903	61,139	252,541
Parent Company [Member] \| Convertible Senior Notes [Member]
Cash paid during the year for interest:
Interest paid										27,283	31,206	13,758
Parent Company [Member] \| Convertible Subordinated Debentures [Member]
Cash paid during the year for interest:
Interest paid										11,833	11,765	11,850
Common Stock Issued in Extinguishment of Debt [Member]
Non-cash financing activity:
Common stock issued										0	95,993	117,463
Common Stock Issued in Extinguishment of Debt [Member] \| Parent Company [Member]
Non-cash financing activity:
Common stock issued										0	95,993	117,463
Common Stock Issued to Settle Warrants That Have Expired [Member]
Non-cash financing activity:
Common stock issued										48	0	0
Common Stock Issued to Settle Warrants That Have Expired [Member] \| Parent Company [Member]
Non-cash financing activity:
Common stock issued										$ 48	$ 0	$ 0