Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings [Member]
Balance, beginning of period at Dec. 31, 2018		$ 427		$ 1,489,520	$ (28,434)
Repurchases of common stock		(10)	$ (17,947)	(99,451)
Share-based compensation			17,950
Net issuance of common stock		3	(3)
Net income	$ 176,611			176,611
Dividends				(29,145)
Change in foreign currency translation adjustment,net of income taxes					12,806
Change in net unrealized investment gains (losses) during the period, net of income taxes					63,598
Balance, end of period at Jun. 30, 2019	$ 1,585,925	420		1,537,535	47,970
Dividends declared per share	$ 0.68
Balance, beginning of period at Mar. 31, 2019		424		1,506,943	14,020
Repurchases of common stock		(5)	(4,777)	(52,337)
Share-based compensation			4,778
Net issuance of common stock		1	(1)
Net income	$ 97,446			97,446
Dividends				(14,517)
Change in foreign currency translation adjustment,net of income taxes					6,639
Change in net unrealized investment gains (losses) during the period, net of income taxes					27,311
Balance, end of period at Jun. 30, 2019	$ 1,585,925	420		1,537,535	47,970
Dividends declared per share	$ 0.34
Balance, beginning of period at Dec. 31, 2019	$ 1,652,491	412		1,593,281	58,798
Cumulative effect from the adoption of new accounting standards, net at Dec. 31, 2019	1,593,281					$ (1,240)
Repurchases of common stock	(176,600)	(17)	(18,454)	(163,717)
Share-based compensation			18,456
Net issuance of common stock		2	(2)
Net income	173,979			173,979
Dividends				(32,614)
Change in foreign currency translation adjustment,net of income taxes					(15,367)
Change in net unrealized investment gains (losses) during the period, net of income taxes					29,163
Balance, end of period at Jun. 30, 2020	$ 1,642,680	397		1,569,689	72,594
Dividends declared per share	$ 0.80
Balance, beginning of period at Mar. 31, 2020		405		1,565,803	(36,094)
Repurchases of common stock		(9)	(4,963)	(81,540)
Share-based compensation			4,964
Net issuance of common stock		1	$ (1)
Net income	$ 101,510			101,510
Dividends				(16,084)
Change in foreign currency translation adjustment,net of income taxes					13,644
Change in net unrealized investment gains (losses) during the period, net of income taxes					95,044
Balance, end of period at Jun. 30, 2020	$ 1,642,680	$ 397		$ 1,569,689	$ 72,594
Dividends declared per share	$ 0.40