Fair Value of Assets and Liabilities - Debt Fair Value (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Senior Unsecured Notes, due 2021 at 4.25%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.25%	4.25%
Senior Unsecured Notes, due 2022 at 5.00%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	5.00%	5.00%
Senior Unsecured Notes, due 2023 at 4.50%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.50%	4.50%
Senior Unsecured Notes, due 2024 at 4.65%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.65%	4.65%
Senior Unsecured Notes, due 2024 at 4.35%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.35%	4.35%
Senior Unsecured Notes, due 2025 at 4.50%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.50%	4.50%
Senior Unsecured Notes, due 2026 at 5.25%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	5.25%	5.25%
Senior Unsecured Notes, due 2026 at 4.75%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.75%	4.75%
Senior Unsecured Notes, due 2027 at 4.95%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.95%	4.95%
Senior Unsecured Notes, due 2028 at 3.95%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	3.95%	3.95%
Senior Unsecured Notes, due 2029 at 4.95%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.95%	4.95%
Senior Unsecured Notes, due 2030 at 4.375%
Fair Value of Assets and Liabilities
Interest rate, stated percentage	4.375%	4.375%
Carrying value
Fair Value of Assets and Liabilities
Total financial liabilities	$ 5,290,396	$ 5,287,658
Carrying value | Senior Unsecured Notes, due 2021 at 4.25%
Fair Value of Assets and Liabilities
Total financial liabilities	398,739	398,379
Carrying value | Senior Unsecured Notes, due 2022 at 5.00%
Fair Value of Assets and Liabilities
Total financial liabilities	497,124	496,821
Carrying value | Senior Unsecured Notes, due 2023 at 4.50%
Fair Value of Assets and Liabilities
Total financial liabilities	499,473	499,432
Carrying value | Senior Unsecured Notes, due 2024 at 4.65%
Fair Value of Assets and Liabilities
Total financial liabilities	348,396	348,295
Carrying value | Senior Unsecured Notes, due 2024 at 4.35%
Fair Value of Assets and Liabilities
Total financial liabilities	818,443	818,075
Carrying value | Senior Unsecured Notes, due 2025 at 4.50%
Fair Value of Assets and Liabilities
Total financial liabilities	346,602	346,431
Carrying value | Senior Unsecured Notes, due 2026 at 5.25%
Fair Value of Assets and Liabilities
Total financial liabilities	343,366	343,083
Carrying value | Senior Unsecured Notes, due 2026 at 4.75%
Fair Value of Assets and Liabilities
Total financial liabilities	446,058	445,905
Carrying value | Senior Unsecured Notes, due 2027 at 4.95%
Fair Value of Assets and Liabilities
Total financial liabilities	394,838	394,649
Carrying value | Senior Unsecured Notes, due 2028 at 3.95%
Fair Value of Assets and Liabilities
Total financial liabilities	391,046	390,759
Carrying value | Senior Unsecured Notes, due 2029 at 4.95%
Fair Value of Assets and Liabilities
Total financial liabilities	417,505	417,307
Carrying value | Senior Unsecured Notes, due 2030 at 4.375%
Fair Value of Assets and Liabilities
Total financial liabilities	388,806	388,522
Fair value
Fair Value of Assets and Liabilities
Total financial liabilities	4,080,549	5,499,211
Fair value | Senior Unsecured Notes, due 2021 at 4.25%
Fair Value of Assets and Liabilities
Total financial liabilities	389,728	406,838
Fair value | Senior Unsecured Notes, due 2022 at 5.00%
Fair Value of Assets and Liabilities
Total financial liabilities	369,308	526,500
Fair value | Senior Unsecured Notes, due 2023 at 4.50%
Fair Value of Assets and Liabilities
Total financial liabilities	356,455	520,478
Fair value | Senior Unsecured Notes, due 2024 at 4.65%
Fair Value of Assets and Liabilities
Total financial liabilities	255,073	364,277
Fair value | Senior Unsecured Notes, due 2024 at 4.35%
Fair Value of Assets and Liabilities
Total financial liabilities	619,191	848,847
Fair value | Senior Unsecured Notes, due 2025 at 4.50%
Fair Value of Assets and Liabilities
Total financial liabilities	232,694	361,783
Fair value | Senior Unsecured Notes, due 2026 at 5.25%
Fair Value of Assets and Liabilities
Total financial liabilities	257,297	369,185
Fair value | Senior Unsecured Notes, due 2026 at 4.75%
Fair Value of Assets and Liabilities
Total financial liabilities	314,674	464,315
Fair value | Senior Unsecured Notes, due 2027 at 4.95%
Fair Value of Assets and Liabilities
Total financial liabilities	357,354	414,012
Fair value | Senior Unsecured Notes, due 2028 at 3.95%
Fair Value of Assets and Liabilities
Total financial liabilities	293,268	393,940
Fair value | Senior Unsecured Notes, due 2029 at 4.95%
Fair Value of Assets and Liabilities
Total financial liabilities	331,351	434,248
Fair value | Senior Unsecured Notes, due 2030 at 4.375%
Fair Value of Assets and Liabilities
Total financial liabilities	$ 304,156	$ 394,788